Java Developer Temple

Open hiper link with new tab or window

2012-01-21T12:20:00.000-08:00

The addition of the TARGET attribute to a hyperlink lets you dictate where the linked page opens.

target="_blank" Opens the linked page in a new tab or window.
target="_self" Opens the linked page in the same tab or window.. This is the default for ordinary pages and doesn't need to be specified. It has a use when working with frames.
target="_parent" Opens the linked page in the parent frame in a frames page.
target="_top" Opens the linked page in a full (i.e. top level) window when used in frames pages. This one is useful for letting a linked page 'break out' of a frame.

Artifactory - Advanced repository manager.

2012-01-21T12:02:00.000-08:00

Please visit the configuration page

How to Find All Unread Messages in Gmail

2012-01-13T04:19:00.000-08:00

we have two ways:

A. To view all (and only) unread messages in your Gmail account:

Type "is:unread" (or "label:unread") (not including the quotation marks) in the Gmail search field.
Click Search Mail.

B. There is a way faster:

Choose Settings-> filters.
Filters-> Create a new Filter
Write: " is: unread" ( without quotes)-> Next( you can use test search before clicking Next)
Ok( there is a box appearing, but click OK if you see)
the key is: you can see many options for filters
if you want to delete it-> check the Delete it box
And Remember to check the Also Apply Filter to..( it will be easier to delate a large number of emails at once)
You should delete the filter once you finish since it will delete your new emails

jQuery in short

2012-01-11T08:12:00.000-08:00

What is jQuery?

jQueryis a library of JavaScript Functions.

jQueryis a lightweight "write less, do more" JavaScript library.

ThejQuery library contains the following features:

HTML element selections
HTML element manipulation
CSS manipulation
HTML event functions
JavaScript Effects and animations
HTML DOM traversal and modification
AJAX
Utilities

Adding the jQueryLibrary to Your Pages

The jQuery library is stored as a single JavaScript file, containing all the jQuery methods.
It can be added to a web page with the following mark-up:

Basic jQuery Example

Downloading jQuery

Twoversions of jQuery are available for downloading: one minified and oneuncompressed (for debugging or reading).

Bothversions can be downloaded from jQuery.com.

Alternatives toDownloading

Ifyou don't want to store the jQuery library on your own computer, you can usethe hosted jQuery library from Google or Microsoft.

The Document ReadyFunction

Youmight have noticed that all jQuery methods, in our examples, are inside adocument.ready() function:

This isto prevent any jQuery code from running before the document is finished loading(is ready).

jQuerySyntax

The jQuery syntax is tailor made forselecting HTML elements and perform some action on the element(s).

Basic syntax is: $(selector).action()

•A dollar sign to define jQuery

•A (selector) to "query (orfind)" HTML elements

•A jQuery action() to be performed on theelement(s)

Examples:

$(this).hide() - hides current element

$("p").hide() - hides allparagraphs

$("p.test").hide() - hides allparagraphs with class="test"

$("#test").hide() - hides theelement with id="test"

jQuery Selectors

Useour excellent jQuery Selector Tester to experiment with the differentselectors.

Selector	Example	Selects
*	$("*")	All elements
#id	$("#lastname")	The element with id=lastname
.class	$(".intro")	All elements with class="intro"
element	$("p")	All p elements
.class.class	$(".intro.demo")	All elements with the classes "intro" and "demo"

:first	$("p:first")	The first p element
:last	$("p:last")	The last p element
:even	$("tr:even")	All even tr elements
:odd	$("tr:odd")	All odd tr elements

:eq(index)	$("ul li:eq(3)")	The fourth element in a list (index starts at 0)
:gt(no)	$("ul li:gt(3)")	List elements with an index greater than 3
:lt(no)	$("ul li:lt(3)")	List elements with an index less than 3
:not(selector)	$("input:not(:empty)")	All input elements that are not empty

:header	$(":header")	All header elements h1, h2 ...
:animated	$(":animated")	All animated elements

:contains(text)	$(":contains('W3Schools')")	All elements which contains the text
:empty	$(":empty")	All elements with no child (elements) nodes
:hidden	$("p:hidden")	All hidden p elements
:visible	$("table:visible")	All visible tables

s1,s2,s3	$("th,td,.intro")	All elements with matching selectors

[attribute]	$("[href]")	All elements with a href attribute
[attribute=value]	$("[href='default.htm']")	All elements with a href attribute value equal to "default.htm"
[attribute!=value]	$("[href!='default.htm']")	All elements with a href attribute value not equal to "default.htm"
[attribute$=value]	$("[href$='.jpg']")	All elements with a href attribute value ending with ".jpg"

:input	$(":input")	All input elements
:text	$(":text")	All input elements with type="text"
:password	$(":password")	All input elements with type="password"
:radio	$(":radio")	All input elements with type="radio"
:checkbox	$(":checkbox")	All input elements with type="checkbox"
:submit	$(":submit")	All input elements with type="submit"
:reset	$(":reset")	All input elements with type="reset"
:button	$(":button")	All input elements with type="button"
:image	$(":image")	All input elements with type="image"
:file	$(":file")	All input elements with type="file"

:enabled	$(":enabled")	All enabled input elements
:disabled	$(":disabled")	All disabled input elements
:selected	$(":selected")	All selected input elements
:checked	$(":checked")	All checked input elements

jQuery Effects

Hereare some examples of effect functions in jQuery:

Method	Description
animate()	Performs a custom animation (of a set of CSS properties) for selected elements
clearQueue()	Removes all queued functions for the selected element
delay()	Sets a delay for all queued functions for the selected element
dequeue()	Runs the next queued functions for the selected element
fadeIn()	Gradually changes the opacity, for selected elements, from hidden to visible
fadeOut()	Gradually changes the opacity, for selected elements, from visible to hidden
fadeTo()	Gradually changes the opacity, for selected elements, to a specified opacity
fadeToggle()
hide()	Hides selected elements
queue()	Shows the queued functions for the selected element
show()	Shows hidden selected elements
slideDown()	Gradually changes the height, for selected elements, from hidden to visible
slideToggle()	Toggles between slideUp() and slideDown() for selected elements
slideUp()	Gradually changes the height, for selected elements, from visible to hidden
stop()	Stops a running animation on selected elements
toggle()	Toggles between hide() and show(), or custom functions, for selected elements
Function	Description
$(selector).hide()	Hide selected elements
$(selector).show()	Show selected elements
$(selector).toggle()	Toggle (between hide and show) selected elements
$(selector).slideDown()	Slide-down (show) selected elements
$(selector).slideUp()	Slide-up (hide) selected elements
$(selector).slideToggle()	Toggle slide-up and slide-down of selected elements
$(selector).fadeIn()	Fade in selected elements
$(selector).fadeOut()	Fade out selected elements
$(selector).fadeTo()	Fade out selected elements to a given opacity
$(selector).animate()	Run a custom animation on selected element

jQueryCallback Functions

A callback function isexecuted after the current animation is 100% finished.

jQuery CallbackFunctions

JavaScriptstatements are executed line by line. However, with animations, the next lineof code can be run even though the animation is not finished. This can createerrors.

Toprevent this, you can create a callback function.

Acallback function is executed after the current animation (effect) is finished.

Typicalsyntax: $(selector).hide(speed,callback)

Thecallback parameter is a function to be executed after the hide effect iscompleted:

jQueryHTML Manipulation

jQuery containspowerful methods (functions) for changing and manipulating HTML elements andattributes.

jQuery HTML Methods

Thefollowing table lists all the methods used to manipulate the DOM.

Themethods below work for both HTML and XML documents. Exception: the html()method.

Method	Description
addClass()	Adds one or more classes (for CSS) to selected elements
after()	Inserts content after selected elements
append()	Inserts content at the end of (but still inside) selected elements
appendTo()	Inserts content at the end of (but still inside) selected elements
attr()	Sets or returns an attribute and value of selected elements
before()	Inserts content before selected elements
clone()	Makes a copy of selected elements
detach()	Removes (but keeps a copy of) selected elements
empty()	Removes all child elements and content from selected elements
hasClass()	Checks if any of the selected elements have a specified class (for CSS)
html()	Sets or returns the content of selected elements
insertAfter()	Inserts HTML markup or elements after selected elements
insertBefore()	Inserts HTML markup or elements before selected elements
prepend()	Inserts content at the beginning of (but still inside) selected elements
prependTo()	Inserts content at the beginning of (but still inside) selected elements
remove()	Removes selected elements
removeAttr()	Removes an attribute from selected elements
removeClass()	Removes one or more classes (for CSS) from selected elements
replaceAll()	Replaces selected elements with new content
replaceWith()	Replaces selected elements with new content
text()	Sets or returns the text content of selected elements
toggleClass()	Toggles between adding/removing one or more classes (for CSS) from selected elements
unwrap()	Removes the parent element of the selected elements
val()	Sets or returns the value attribute of the selected elements (form elements)
wrap()	Wraps specified HTML element(s) around each selected element
wrapAll()	Wraps specified HTML element(s) around all selected elements
wrapInner()	Wraps specified HTML element(s) around the content of each selected element

jQueryCSS Manipulation

jQueryhas one important method for CSS manipulation: css()

Thecss() method has three different syntaxes, to perform different tasks.

css(name) - Return CSS property value
css(name,value) - Set CSS property and value
css({properties}) - Set multiple CSS properties and values

$("p").css({"background-color":"yellow","font-size":"200%"});

$("#div1").height("200px");

$("#div2").width("300px");

CSS Properties	Description
$(selector).css(name)	Get the style property value of the first matched element
$(selector).css(name,value)	Set the value of one style property for matched elements
$(selector).css({properties})	Set multiple style properties for matched elements
$(selector).height(value)	Set the height of matched elements
$(selector).width(value)	Set the width of matched elements

jQuery CSS Methods

Thefollowing table lists all the methods used to manipulate CSS properties.

Method	Description
addClass()	Adds one or more classes to selected elements
css()	Sets or returns one or more style properties for selected elements
hasClass()	Checks if any of the selected elements have a specified class
height()	Sets or returns the height of selected elements
offset()	Sets or returns the position (relative to the document) for selected elements
offsetParent()	Returns the first parent element that is positioned
position()	Returns the position (relative to the parent element) of the first selected element
removeClass()	Removes one or more classes from selected elements
scrollLeft()	Sets or returns the horizontal position of the scrollbar for the selected elements
scrollTop()	Sets or returns the vertical position of the scrollbar for the selected elements
toggleClass()	Toggles between adding/removing one or more classes from selected elements
width()	Sets or returns the width of selected elements

jQueryEvent Methods

Eventmethods trigger, or bind a function to an event for all matching elements.

Trigger example:

$("button").click()- triggers the click event for a button element.

Binding example:

$("button").click(function(){$("img").hide()})- binds a function to the click event.

Eventmethods trigger, or bind a function to an event for all matching elements.

Trigger example:

$("button").click()- triggers the click event for a button element.

Binding example:

$("button").click(function(){$("img").hide()})- binds a function to the click event.

Thefollowing table lists all the methods used to handle events.

Method	Description
bind()	Add one or more event handlers to matching elements
blur()	Triggers, or binds a function to the blur event of selected elements
change()	Triggers, or binds a function to the change event of selected elements
click()	Triggers, or binds a function to the click event of selected elements
dblclick()	Triggers, or binds a function to the dblclick event of selected elements
delegate()	Add one or more event handlers to current, or future, specified child elements of the matching elements
die()	Remove all event handlers added with the live() function
error()	Triggers, or binds a function to the error event of selected elements
event.currentTarget	The current DOM element within the event bubbling phase
event.data	Contains the optional data passed to jQuery.fn.bind when the current executing handler was bound
event.isDefaultPrevented()	Returns whether event.preventDefault() was called for the event object
event.isImmediatePropagationStopped()	Returns whether event.stopImmediatePropagation() was called for the event object
event.isPropagationStopped()	Returns whether event.stopPropagation() was called for the event object
event.pageX	The mouse position relative to the left edge of the document
event.pageY	The mouse position relative to the top edge of the document
event.preventDefault()	Prevents the default action of the event
event.relatedTarget	The other DOM element involved in the event, if any
event.result	This attribute contains the last value returned by an event handler that was triggered by this event, unless the value was undefined
event.stopImmediatePropagation()	Prevents other event handlers from being called
event.stopPropagation()	Prevents the event from bubbling up the DOM tree, preventing any parent handlers from being notified of the event
event.target	The DOM element that initiated the event
event.timeStamp	This attribute returns the number of milliseconds since January 1, 1970, when the event is triggered
event.type	Describes the nature of the event
event.which	Which key or button was pressed for a key or button event
focus()	Triggers, or binds a function to the focus event of selected elements
focusin()	Binds a function to the focusin event of selected elements
focusout()	Binds a function to the focusout event of selected elements
hover()	Binds one or two functions to the hover event of selected elements
keydown()	Triggers, or binds a function to the keydown event of selected elements
keypress()	Triggers, or binds a function to the keypress event of selected elements
keyup()	Triggers, or binds a function to the keyup event of selected elements
live()	Add one or more event handlers to current, or future, matching elements
load()	Triggers, or binds a function to the load event of selected elements
mousedown()	Triggers, or binds a function to the mouse down event of selected elements
mouseenter()	Triggers, or binds a function to the mouse enter event of selected elements
mouseleave()	Triggers, or binds a function to the mouse leave event of selected elements
mousemove()	Triggers, or binds a function to the mouse move event of selected elements
mouseout()	Triggers, or binds a function to the mouse out event of selected elements
mouseover()	Triggers, or binds a function to the mouse over event of selected elements
mouseup()	Triggers, or binds a function to the mouse up event of selected elements
one()	Add one or more event handlers to matching elements. This handler can only be triggered once per element
ready()	Binds a function to the ready event of a document (when an HTML document is ready to use)
resize()	Triggers, or binds a function to the resize event of selected elements
scroll()	Triggers, or binds a function to the scroll event of selected elements
select()	Triggers, or binds a function to the select event of selected elements
submit()	Triggers, or binds a function to the submit event of selected elements
toggle()	Binds two or more functions to the toggle between for the click event for selected elements
trigger()	Triggers all events bound to the selected elements
triggerHandler()	Triggers all functions bound to a specified event for the selected elements
unbind()	Remove an added event handler from selected elements
undelegate()	Remove an event handler to selected elements, now or in the future
unload()	Triggers, or binds a function to the unload event of selected elements

What is AJAX?

AJAX = Asynchronous JavaScript and XML.

AJAX is a technique for creating fast and dynamic web pages.

AJAX allows web pages to be updated asynchronously by exchanging small amountsof data with the server behind the scenes. This means that it is possible toupdate parts of a web page, without reloading the whole page.

AJAX and jQuery

jQueryprovides a rich set of methods for AJAX web development.

WithjQuery AJAX, you can request TXT, HTML, XML or JSON data from a remote serverusing both HTTP Get and HTTP Post.

And you can load remote data directly into selected HTML elementsof your web page!

Write Less, Do More

ThejQuery load() method is a simple (but very powerful) AJAX function. It has thefollowing syntax:

$(selector).load(url,data,callback)

Usethe selector to define the HTML element(s) to change, and the urlparameter to specify a web address for your data.

Onlyif you want to send data to the server, you need to use the dataparameter. Only if you need to trigger a function after completion, you willuse the callback parameter.

Low Level AJAX

$.ajax(options)is the syntax of the low level AJAX function.

$.ajaxoffers more functionality than higher level functions like load, get, and post,but it is also more difficult to use.

Theoption parameter takes name|value pairs defining url data, passwords, datatypes, filters, character sets, timeout and error functions.

Request	Description
$(selector).load(url,data,callback)	Load remote data into selected elements
$.ajax(options)	Load remote data into an XMLHttpRequest object

jQuery AJAX Methods

AJAXis the art of exchanging data with a server, and update parts of a web page -without reloading the whole page.

Thefollowing table lists all the jQuery AJAX methods:

Method	Description
$.ajax()	Performs an AJAX request
ajaxComplete()	Specifies a function to run when the AJAX request completes
ajaxError()	Specifies a function to run when the AJAX request completes with an error
ajaxSend()	Specifies a function to run before the AJAX request is sent
$.ajaxSetup()	Sets the default values for future AJAX requests
ajaxStart()	Specifies a function to run when the first AJAX request begins
ajaxStop()	Specifies a function to run when all AJAX requests have completed
ajaxSuccess()	Specifies a function to run an AJAX request completes successfully
$.get()	Loads data from a server using an AJAX HTTP GET request
$.getJSON()	Loads JSON-encoded data from a server using a HTTP GET request
$.getScript()	Loads (and executes) a JavaScript from the a server using an AJAX HTTP GET request
load()	Loads data from a server and puts the returned HTML into the selected element
$.param()	Creates a serialized representation of an array or object (can be used as URL query string for AJAX requests)
$.post()	Loads data from a server using an AJAX HTTP POST request
serialize()	Encodes a set of form elements as a string for submission
serializeArray()	Encodes a set of form elements as an array of names and values

JQuery versus Dojo versus YUI
In search for a reliable open source javascript library/framework that works cross-browser, I came across the following:

    JQuery
    YUI (The Yahoo! User Interface Library)
    Dojo Toolkit

JQuery

Pros:
- JQuery is the most popular one of them all.
- It is very easy to use and to understand.
- The core library is only 15Kb in size.
- Their statement is: ‘The Write Less, Do More, Javascript Library’.

Cons:
- Hard to use with object oriented programming
- JQuery supports plug-ins, but all these plug-ins are not verified.
- JQuery is a library

YUI

Pros:
- It is developed by Yahoo
- Fully documented, with a great API browser
- Very consistent and reliable
- Also contains unit testing framework
- YUI is a framework

Cons:
- Heavy page weight
- Very few utility or helper functions/methods
- Lacks the use of chaining methods together

Dojo Toolkit

Pros:
- Debug your code in Firebug
- Dojo integrated in Zend Framework
- Hierarchical package system speeds loading
- Dojo is a framework

Cons:
- Dojo fails in online documentation

Taking Video Screenshot with VLC Player

2012-01-08T07:10:00.000-08:00

VLC media player comes with inbuilt feature to take video snapshot. To capture screenshot you must have VLC player or you can download it from here.

Capturing Screenshot of Video vlc-video-menu

1. Open your video on VLC media player.
2. Pause your video to the point for which you need to capture image.
3. On Video menu click Snapshot (Menu bar –> Video –> Snapshot) or default shortcut SHIFT + S
4. Your image is saved
5. You can access your image from default store location.
6. To change default storage location go to Menu –> Tools –> Preference
7. Under Preference –> Video –> Video Snapshot section. Change your location.

How to handle One apostrophe in SQL string

2011-09-29T23:11:00.000-07:00

If you are using SQL strings in your database operations, chances are you have come across problem with strings in SQL statement. One apostrophe screws up the SQL string, causing the SQL statement to fail.

Assume you have a SQL string:
SELECT * FROM tUsers WHERE LastName='O'Brien';
When LastName contains a name like O'Brien, the final string becomes

The second ' ends the SQL statement, leaving the rest of the string dangling. The solution is easy: Replace each ' in O'Brien with two 's, something like O''Brien, so the final SQL looks like:

SELECT * FROM tUsers WHERE LastName='O''Brien';
The second ' "escapes" the third ', thus leaving the whole SQL statement complete.

Difference between Shallow Copy and Deep Copy

2011-08-06T12:36:00.000-07:00

Shallow Copy
This is a result of the default cloning functionality provided by the Object.clone() method if the class has non-primitive data type members as well. Shallow Copy concept is not applicable to the classes having only primitive data type members as in that case the default cloning will also result into a Deep Copy only.

In case of Shallow Copy, the cloned object also refers to the same object to which the original object refers as only the object references gets copied and not the referred objects themselves. That's why the name Shallow Copy. Read more about Cloning More Details
sample program :
package com.sallowcopy;
/**
*
* @author thanooj
*
*/
class Person implements Cloneable {
// Lower-level object
private Car car;
private String name;
private Integer no;

public Car getCar() {
return car;
}
public String getName() {
return name;
}
public void setName(String s) {
name = s;
}
public Person(Integer n, String s, String t) {
no = n;
name = s;
car = new Car(t);
}
public Object clone() {
// shallow copy
try {
return super.clone();
} catch (CloneNotSupportedException e) {
return null;
}
}
public void setNo(Integer no) {
this.no = no;
}
public Integer getNo() {
return no;
}
}

class Car {

private String name;

public String getName() {
return name;
}
public void setName(String s) {
name = s;
}
public Car(String s) {
name = s;
}
}

public class ShallowCopyTest {

public static void main(String[] args) {
// Original Object
Person p = new Person(new Integer(1000), "sreeRama", "Garuda");
System.out.println("Original (orginal values): " + p.getNo() + " "
+ p.getName() + " - " + p.getCar().getName());
// Clone as a shallow copy
Person q = (Person) p.clone();
System.out.println("Clone (before change): " + q.getNo() + " "
+ q.getName() + " - " + q.getCar().getName());
// change the primitive member
q.setName("Indra");
q.setNo(new Integer(2000));
// change the lower-level object
q.getCar().setName("Iravath");
System.out.println("Clone (after change): " + q.getNo() + " "
+ q.getName() + " - " + q.getCar().getName());
System.out.println("Original (after clone is modified): " + p.getNo()
+ " " + p.getName() + " - " + p.getCar().getName());
}
}
//output :
Original (orginal values): 1000 sreeRama - Garuda
Clone (before change): 1000 sreeRama - Garuda
Clone (after change): 2000 Indra - Iravath
Original (after clone is modified): 1000 sreeRama - Iravath
-------------------------------------------
Deep Copy

We need to override the clone() method for the classes having non-primitive type members to achieve Deep Copy as Deep Copy requires the member objects to be cloned as well, which is not done by the default cloning mechanism. Why is it not done by the default cloning? Because clone() is a method of the Object class and at that level it's not known what a typical class can have as its members and hence only a field-by-field copy approach has been provided as the default cloning mechanism.

Implementing Deep Copy in Java

For Deep Copy, we need to ensure that the member classes also implement the Cloneable interface otherwise calling the clone() method on the objects of those classes will result into CloneNotSupportedException. So, to implement Deep Copy, we first need to ensure that all the member classes (at all the levels - like if the member class itself has a member of some class type then that class as well... and so on) are implementing the Cloneable interface. After that we override the clone() method in all those classes (even in the classes where we have only primitive type members otherwise we would not be able to call the protected clone()method of Object class on the instances of those classes inside some other class ... a typical restriction of the protected access. We'll cover this in a separate article) and finally calling clone() method on the object members in the overriden clone() method definition.
sample program :

package com.deepcopy;
/**
*
* @author thanooj
*
*/
class Person implements Cloneable {
// Lower-level object
private Car car;
private String name;

public Car getCar() {
return car;
}
public String getName() {
return name;
}
public void setName(String s) {
name = s;
}
public Person(String s, String t) {
name = s;
car = new Car(t);
}
public Object clone() throws CloneNotSupportedException{
// Deep copy
Person p = (Person) super.clone();
p.car = (Car) p.car.clone();
return p;
}
}
class Car implements Cloneable{

private String name;

public String getName() {
return name;
}
public void setName(String s) {
name = s;
}
public Car(String s) {
name = s;
}
@Override
protected Object clone() throws CloneNotSupportedException {
return super.clone();
}
}
public class DeepCopyTest {

public static void main(String[] args) {
// Original Object - before Deep cloning
Person p = new Person("sreeRama", "Garuda");
System.out.println(p.getName()+" "+p.getCar().getName());
Person pClone = null;
try {
pClone = (Person) p.clone();
} catch (CloneNotSupportedException e) {
e.printStackTrace();
}
System.out.println("Clone (before change): "+pClone.getName()+" "+pClone.getCar().getName());
pClone.setName("Indra");
pClone.getCar().setName("Iravath");
System.out.println("Clone (after change): "+pClone.getName()+" "+pClone.getCar().getName());
// Original Object - after Deep cloning
System.out.println(p.getName()+" "+p.getCar().getName());
}
}
// Output :
sreeRama Garuda
Clone (before change): sreeRama Garuda
Clone (after change): Indra Iravath
sreeRama Garuda

MySQL import and export

2011-06-25T13:01:00.000-07:00

Here are few MySQL Queries/commands that i regularly use for exporting and importing MySQL data. This is for my reference, but just thought this might be useful for newbies.
MySQL Table Data Export and Import

To export the just table data please use the following query
SELECT * INTO OUTFILE 'data.txt' FIELDS TERMINATED BY ',' FROM mytable;
To import the csv file into table execute the following SQL Query.
LOAD DATA INFILE 'data.txt' INTO TABLE mytable FIELDS TERMINATED BY ',';

Copy the contents of one database to another

First, create the new database
create database db2;
Then, from the command-line, do the following to copy the contents from db1 to db2.
$ mysqldump -u root --password=pass db1 | mysql -u root --password=pass db2

MySQL Dump

To export the MySQL database into a dump file, please execute the following command
$ mysqldump -u root --password=pass db1 > dbdump.sql

Create MySQL User

Creating MySQL user and granting access
CREATE USER 'myuser'@'localhost' IDENTIFIED BY 'myuser';
GRANT ALL ON *.* TO 'myuser'@'localhost' IDENTIFIED BY 'myuser';

What is serialVersionUID?

2011-06-21T08:02:00.000-07:00

Most people learn about serialVersionUID after they write their first serializable object (I know I did). You add ‘implements Serializable’ and in the next moment your IDE starts complaining… so what’s up?

Lets look at a simple example to see what meaning that variable has. In the example we will use the class SerializeMe shown below:

class SerializeMe implements Serializable {
private static final long serialVersionUID = 1L;

private int data;

public SerializeMe (int data) {
this.data = data;
}

public int getData() {
return data;
}
}

Field data represents some information stored in the class. Class implements the Serializable interface, so my IDE automatically offered me to declare the serialVersionUID field. Lets start with value 1 set there.

We will also need some class that will serialize and deserialize the SerializeMe class. Here it is:

public class UIDTester {
public static void main(String... strings) throws Exception {
File file = new File("out.ser");
FileOutputStream fos = new FileOutputStream(file);
ObjectOutputStream oos = new ObjectOutputStream(fos);

SerializeMe serializeMe = new SerializeMe(1);
oos.writeObject(serializeMe);
oos.close();

FileInputStream fis = new FileInputStream(file);
ObjectInputStream ois = new ObjectInputStream(fis);

SerializeMe dto = (SerializeMe) ois.readObject();
System.out.println("data : " + dto.getData());
ois.close();
}
}

This code will serialize an instance of class SerializeMe to a file and then deserialize it back. Now let’s run the main function! You should get output that says:
data : 1

It means that our object was properly serialized and deserialized. Note that the file “out.ser” was created on disk and it is still there even after the program finished. Let’s see if we can read that file once again, this time without creating it first. To do that, comment out lines from 4 to 9 in the UIDTester class:

public class UIDTester {
public static void main(String... strings) throws Exception {
File file = new File("out.ser");
//FileOutputStream fos = new FileOutputStream(file);
//ObjectOutputStream oos = new ObjectOutputStream(fos);

//SerializeMe serializeMe = new SerializeMe(1);
//oos.writeObject(serializeMe);
//oos.close();

FileInputStream fis = new FileInputStream(file);
ObjectInputStream ois = new ObjectInputStream(fis);

SerializeMe dto = (SerializeMe) ois.readObject();
System.out.println("data : " + dto.getData());
ois.close();
}
}

This way, the main method starts right away with reading the file from the disk and deserializing data stored in it. As the file is exactly the same and our class didn’t changed either, we should get exactly the same output:

data : 1

Now, let’s see what happens, when we change the serialVersionUID value and try to deserialize once again our file. Change the line 2 in the class SerializeMe so that serialVersionUID contains now 2 instead of 1:

private static final long serialVersionUID = 2L;

Now let’s run again our program (just like one step before, with commented out lines writing the file). We should get an exception like this:

Exception in thread "main" java.io.InvalidClassException:
SerializeMe; local class incompatible: stream classdesc
serialVersionUID = 1, local class serialVersionUID = 2

As you can see, this time the deserialization didn’t go well. ObjectInputStream complained about the serialVersionUID being changed. How does he know that it changed? If serialVersinUID is static, then it should not have been serialized in the first place, and there should be no information about the previous value 1 during the deserialization, right? Well, serialVersionUID is an exception to the rule that “static fields don’t get serialized”. ObjectOutputStream writes every time the value of serialVersionUID to the output stream. ObjectInputStream reads it back and if the value read from the stream does not agree with the serialVersionUID value in the current version of the class, then it throws the InvalidClassException. Moreover, if there is no serialVersionUID officially declared in the class to be serialized, compiler automatically adds it with a value generated based on the fields declared in the class.

So what is it for after all? Let’s suppose that there is some file storing a serialized object of some class A. The deserialization of that object does not necessarily have to occur exactly after serialization. It can occur after a few months or on a completely different JVM (i.e. sending an object through net using serialization). In both cases, there is a chance that the class declaration has changed between serialization and deserialization. It would be nice to have some kind of versioning system for every serializable class – and serialVersionUID does exactly that. It checks if the data read from the input stream is compatible with the current definition of the class.

If so, then why is it recommended to specify your own serialVersionUID ? It gives us simply more control. Default rules for generating serialVersionUID can be too strict in some cases. For example when the visibility of a field changes, the serialVersionUID changes too. Value generated automatically can differ between various Java implementations. There is a chance that some object serialized on one Java implementation will not deserialize on some other Java implementation, even if the class definition is exactly the same. Furthermore, sometimes you just want for some reason to forbid deserialization of old serialized objects, and in this case you just have to change the serialVersionUID.

Now that you know that specifying your own serialVersionUID is recommended, you might tend to write it once for every serializable class ( or have it generated by the IDE ) and forget about it. WRONG !!! If you write it once and don’t take care to update it when necessary, you loose all the merits of serialVersionUID. All your classes will get deserialized without exceptions even when using outdated data. What you should do is to change serialVersionUID (for example increase it by 1 or make your IDE generate automatically a new value) every time there is some change in the definition of data stored in the class. For example if you change data types, variable names or add new data – hence every time you want to have ‘backward incompatibility’ for deserialization.

session tracking techniques in java

2011-06-19T10:04:00.000-07:00

Here we do share session tracking techniques in java

What is a session?
seesion is a scope of accessing a client state in series of continuous request and response with in a browser window.

Why should a session be maintained?
When there is a series of continuous request and response from a same client to a server, the server cannot identify from which client it is getting requests. Because HTTP is a stateless protocol.

When there is a need to maintain the conversational state, session tracking is needed. For example, in a shopping cart application a client keeps on adding items into his cart using multiple requests. When every request is made, the server should identify in which client’s cart the item is to be added. So in this scenario, there is a certain need for session tracking.

Solution is, when a client makes a request it should introduce itself by providing unique identifier every time. There are five different methods to achieve this.
Session tracking methods:

User authorization
Hidden fields
URL rewriting
Cookies
Session tracking API

The first four methods are traditionally used for session tracking in all the server-side technologies. The session tracking API method is provided by the underlying technology (java servlet or PHP or likewise). Session tracking API is built on top of the first four methods.

1. User Authorization
Users can be authorized to use the web application in different ways. Basic concept is that the user will provide username and password to login to the application. Based on that the user can be identified and the session can be maintained.

2. Hidden Fields

Hidden fields like the above can be inserted in the webpages and information can be sent to the server for session tracking. These fields are not visible directly to the user, but can be viewed using view source option from the browsers. This type doesn’t need any special configuration from the browser of server and by default available to use for session tracking. This cannot be used for session tracking when the conversation included static resources lik html pages.
3. URL Rewriting
Original URL: http://server:port/servlet/ServletName
Rewritten URL: http://server:port/servlet/ServletName?sessionid=7456

and

encodeURL
String encodeURL(String url)
Encodes the specified URL by including the session ID in it, or, if encoding is not needed, returns the URL unchanged. The implementation of this method includes the logic to determine whether the session ID needs to be encoded in the URL. For example, if the browser supports cookies, or session tracking is turned off, URL encoding is unnecessary.

For robust session tracking, all URLs emitted by a servlet should be run through this method. Otherwise, URL rewriting cannot be used with browsers which do not support cookies.

Parameters:
url - the url to be encoded.
Returns:
the encoded URL if encoding is needed; the unchanged URL otherwise.

encodeRedirectURL
String encodeRedirectURL(String url)

Encodes the specified URL for use in the sendRedirect method or, if encoding is not needed, returns the URL unchanged. The implementation of this method includes the logic to determine whether the session ID needs to be encoded in the URL. Because the rules for making this determination can differ from those used to decide whether to encode a normal link, this method is separated from the encodeURL method.

All URLs sent to the HttpServletResponse.sendRedirect method should be run through this method. Otherwise, URL rewriting cannot be used with browsers which do not support cookies.

Parameters:
url - the url to be encoded.
Returns:
the encoded URL if encoding is needed; the unchanged URL otherwise.

When a request is made, additional parameter is appended with the url. In general added additional parameter will be sessionid or sometimes the userid. It will suffice to track the session. This type of session tracking doesn’t need any special support from the browser. Disadvantage is, implementing this type of session tracking is tedious. We need to keep track of the parameter as a chain link until the conversation completes and also should make sure that, the parameter doesn’t clash with other application parameters.

and

String contextPath = request.getContextPath();
String userURL = contextPath + "/default.jsp?name="+userName;
String encodedUrl = response.encodeURL(userURL);
String encodedRedirectURL = response.encodeRedirectURL(userURL);
------
4. Cookies

Cookies are the mostly used technology for session tracking. Cookie is a key value pair of information, sent by the server to the browser. This should be saved by the browser in its space in the client computer. Whenever the browser sends a request to that server it sends the cookie alogwith it. Then the server can identify the client using the cookie.
In java, following is the source code snippet to create a cookie:

// creating a cookie
Cookie user = new Cookie("userName","Sreerama");
response.addCookie(user);
// retriving a cookie
Cookie [] userArray = request.getCookies();
for(Cookie user : userArray){
System.out.println(user.getName());
}

Session tracking is easy to implement and maintain using the cookies. Disadvantage is that, the users can opt to disable cookies using their browser preferences. In such case, the browser will not save the cookie at client computer and session tracking fails.

5. Session tracking API
Session tracking API is built on top of the first four methods. This is inorder to help the developer to minimize the overhead of session tracking. This type of session tracking is provided by the underlying technology. Lets take the java servlet example. Then, the servlet container manages the session tracking task and the user need not do it explicitly using the java servlets. This is the best of all methods, because all the management and errors related to session tracking will be taken care of by the container itself.Every client of the server will be mapped with a javax.servlet.http.HttpSession object. Java servlets can use the session object to store and retrieve java objects across the session. Session tracking is at the best when it is implemented using session tracking api.

// create a session
HttpSession ses = request.getSession(true); // arg- true/false
ses.setAttribute("user",UserObj);
// retrieve a session
HttpSession ses = request.getSession();
User user = (User)ses.getAttribute("user");
it depends on the browser preferences. the servlet tries to set cookies but if they are disabled in browser it moves to session tracking stuff with urlencoding.
// cookies and url rewrite
request.isRequestedSessionIdFromCookie();
request.isRequestedSessionIdFromURL();

simple Session Tracker

2011-06-19T07:59:00.000-07:00

Here we share, how to track a user login as session in a simple way.

Detailed usage of Comparable and Comparator

2011-06-19T06:51:00.000-07:00

Here we do share about Detailed usage of Comparable and Comparator.

-first we do try to understand Detailed usage of Comparable.
// Employee.java
package com.comparable;

public class Employee implements Comparable, Serializable {

private int eNo;
private String eName;
private float eSal;

public Employee() {
super();
}

public Employee(int eNo, String eName, float eSal) {
super();
this.eNo = eNo;
this.eName = eName;
this.eSal = eSal;
}

@Override
public int hashCode() {
System.out.println("-hashCode()- : " + this.hashCode());
final int prime = 31;
int result = 1;
result = prime * result + ((eName == null) ? 0 : eName.hashCode());
result = prime * result + eNo;
result = prime * result + Float.floatToIntBits(eSal);
return result;
}

@Override
public boolean equals(Object obj) {
System.out.println("-equals(obj)-: " + obj.toString());
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
Employee other = (Employee) obj;
if (eName == null) {
if (other.eName != null)
return false;
} else if (!eName.equals(other.eName))
return false;
if (eNo != other.eNo)
return false;
if (Float.floatToIntBits(eSal) != Float.floatToIntBits(other.eSal))
return false;
return true;
}

public int geteNo() {
return eNo;
}

public String geteName() {
return eName;
}

public float geteSal() {
return eSal;
}

@Override
public int compareTo(Employee emp) {
int comp = 0;
if ((comp = this.geteName().compareTo(emp.geteName())) != 0) {
} else {
if ((comp = Float.floatToIntBits(this.geteSal())
- Float.floatToIntBits(emp.geteSal())) != 0) {
} else {
comp = this.geteNo() - emp.geteNo();
}
}
return comp;
}
}
//EmpComparable.java
package com.comparable;

/*
* To be able to use the Comparable interface, the class of the objects
* in the collection has to implement that interface.
* You might have for example a List of objects from a class
* that you don't control yourself - for example,
* a class that comes from some third-party library.
* You can't make that class implement Comparable easily
* (it would mean you'd have to change the source code of
* the third-party library, which is normally not a good idea).
* To be able to sort the List anyway, you can implement your own Comparator
* and pass that to for example
* Collections.sort(list, comparator);.
* Your Comparator object can be separate from the objects that are in the List.
*/
import java.util.ArrayList;
import java.util.Collections;

public class EmpComparable {

/**
* @param args
*/
public static void main(String[] args) {

ArrayList empList = EmpComparable.getEmployees();

EmpComparable.EmpListIterate(empList);

}

public static ArrayList getEmployees() {

ArrayList empList = new ArrayList();
empList.add(new Employee(1, "Sreerama", 50000.0f));
empList.add(new Employee(2, "Seetha", 45000.0f));
empList.add(new Employee(8, "Lakshmana", 40000.0f));
empList.add(new Employee(4, "Bharatha", 30000.0f));
empList.add(new Employee(5, "Sethrugna", 20000.0f));
empList.add(new Employee(7, "Hanuma", 10000.0f));
empList.add(new Employee(6, "Hanuma", 15000.0f));
empList.add(new Employee(3, "Lakshmana", 40000.0f));

/*
* perform the sorting on given object; NOTE - no return type.
* we cont perform reverse sorting by using comparable
*/
Collections.sort(empList);

return empList;
}

public static void EmpListIterate(ArrayList empList) {

System.out.println("EmpNo" + "\t\t" + "EmpName" + "\t\t\t" + "EmpSal");
System.out.println("-----" + "\t\t" + "-------" + "\t\t\t" + "------");
// no need of Iterator here, we just go for display employees.
for (Employee emp : empList) {
System.out.println(emp.geteNo() + "\t\t" + emp.geteName() + "\t\t"
+ emp.geteSal());
}

}

}
output:
-------

---------------------------------
-Second, we do try to understand Detailed usage of Comparator.
//Employee.java
package com.comparator;

public class Employee implements Serializable {

private int eNo;
private String eName;
private float eSal;

public Employee() {
super();
}

public Employee(int eNo, String eName, float eSal) {
super();
this.eNo = eNo;
this.eName = eName;
this.eSal = eSal;
}

@Override
public int hashCode() {
System.out.println("-hashCode()- : " + this.hashCode());
final int prime = 31;
int result = 1;
result = prime * result + ((eName == null) ? 0 : eName.hashCode());
result = prime * result + eNo;
result = prime * result + Float.floatToIntBits(eSal);
return result;
}

@Override
public boolean equals(Object obj) {
System.out.println("-equals(obj)-: " + obj.toString());
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
Employee other = (Employee) obj;
if (eName == null) {
if (other.eName != null)
return false;
} else if (!eName.equals(other.eName))
return false;
if (eNo != other.eNo)
return false;
if (Float.floatToIntBits(eSal) != Float.floatToIntBits(other.eSal))
return false;
return true;
}

public int geteNo() {
return eNo;
}

public String geteName() {
return eName;
}

public float geteSal() {
return eSal;
}
}
//EmpComparator.java
package com.comparator;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;

import com.comparable.EmpComparable;
import com.comparable.Employee;

class EmpNameComparator implements Comparator {

@Override
public int compare(Employee emp1, Employee emp2) {
return emp1.geteName().compareTo(emp2.geteName());
}
}
class EmpNoComparator implements Comparator {

@Override
public int compare(Employee emp1, Employee emp2) {
return emp1.geteNo() < emp2.geteNo() ? -1 : (emp1.geteNo() < emp2
.geteNo()) ? 0 : 1;
}
}
class EmpSalComparator implements Comparator {

@Override
public int compare(Employee emp1, Employee emp2) {
return Float.floatToIntBits(emp1.geteSal()) < Float.floatToIntBits(emp2
.geteSal()) ? -1
: (Float.floatToIntBits(emp1.geteSal()) < Float
.floatToIntBits(emp2.geteSal())) ? 0 : 1;
}
}
public class EmpComparator {

public EmpComparator() {
// no code
}
public static Comparator CompareWith(String comp) {
System.out.println("-comp- " + comp);
Comparator compObj = null;
if (comp.equals("EmpName")) {
compObj = new EmpNameComparator();
} else if (comp.equals("EmpSal")) {
compObj = new EmpSalComparator();
} else {
compObj = new EmpNoComparator();
}
return compObj;
}
public static ArrayList showEmployees() {
ArrayList empList = new ArrayList();
empList.add(new Employee(1, "Sreerama", 50000.0f));
empList.add(new Employee(2, "Seetha", 45000.0f));
empList.add(new Employee(8, "Lakshmana", 40000.0f));
empList.add(new Employee(4, "Bharatha", 30000.0f));
empList.add(new Employee(5, "Sethrugna", 20000.0f));
empList.add(new Employee(7, "Hanuma", 10000.0f));
empList.add(new Employee(6, "Hanuma", 15000.0f));
empList.add(new Employee(3, "Lakshmana", 40000.0f));
// perform the sorting on given object; NOTE - no return type.
Collections.sort(empList, EmpComparator.CompareWith("EmpName"));
EmpComparable.EmpListIterate(empList);
Collections.sort(empList, EmpComparator.CompareWith("EmpSal"));
EmpComparable.EmpListIterate(empList);
Collections.sort(empList, EmpComparator.CompareWith("default"));
EmpComparable.EmpListIterate(empList);
//Reverse sort is also possible.
Collections.sort(empList, Collections.reverseOrder(EmpComparator.CompareWith("default")));
EmpComparable.EmpListIterate(empList);
return empList;
}
public static void EmpListIterate(ArrayList empList) {

System.out.println("EmpNo" + "\t\t" + "EmpName" + "\t\t\t" + "EmpSal");
System.out.println("-----" + "\t\t" + "-------" + "\t\t\t" + "------");
// no need of Iterator here, we just go for display employees.
for (Employee emp : empList) {
System.out.println(emp.geteNo() + "\t\t" + emp.geteName() + "\t\t"
+ emp.geteSal());
}
}
public static void main(String[] args) {
ArrayList empList = EmpComparator.showEmployees();

}
}
output:
------

// In reverse order by EmpNo as default sort.

Set session timeout in Weblogic

2011-04-17T22:26:00.000-07:00

There are two ways user's HTTP session timeout can be set for your web application.
1. Web.xml
2. Weblogic.xml

More importantly the timeout value set in web.xml takes precedence over weblogic.xml. If you don't set any values in web.xml, weblogic.xml takes over. I think it is better to handle session timeout in web.xml itself since web.xml takes precedence over application server’s deployment descriptors.

Parse CSV In Java

2011-04-16T23:16:00.000-07:00

package com.csv;

import java.io.BufferedReader;
import java.io.FileReader;
import java.util.StringTokenizer;

public class ParseCSVInJava {

/**
* @param args
*/
public static void main(String[] args) {

try
{
//csv file containing data
String strFile = "D:\\WS12042011\\Parsing_XMLDOM_CSV_Text_In_Java\\src\\com\\csv\\Employee.csv";
//create BufferedReader to read csv file
BufferedReader br = new BufferedReader( new FileReader(strFile));
String strLine = "";
StringTokenizer st = null;
int lineNumber = 0, tokenNumber = 0;
//read comma separated file line by line
while( (strLine = br.readLine()) != null)
{
lineNumber++;
//break comma separated line using ","
st = new StringTokenizer(strLine, ",");
while(st.hasMoreTokens())
{
//display csv values
tokenNumber++;
System.out.println("Line:" + lineNumber +", Token:" + tokenNumber+ ", Value = "+ st.nextToken());
}
//reset token number
tokenNumber = 0;
}
}
catch(Exception e)
{
System.out.println("Exception while reading csv file: " + e);
}

}

}
----------
out put
----------
Line:1, Token:1, Value = one:1
Line:1, Token:2, Value = two:2
Line:1, Token:3, Value = three:3
Line:1, Token:4, Value = four:4
Line:1, Token:5, Value = five:5
Line:1, Token:6, Value = six:6
Line:2, Token:1, Value = parsing
Line:2, Token:2, Value = comma
Line:2, Token:3, Value = separated
Line:2, Token:4, Value = file
Line:2, Token:5, Value = in
Line:2, Token:6, Value = java

Will your resume get you the interview call?

2011-03-25T03:27:00.000-07:00

1. Should your resume have a career goal/ objective statement? A resume that is worthy of representing you, should clearly state your career objective. A career objective is an indirect way of advertising what all you would bring to the company/ role. It must display a ‘giving’ attitude and not a ‘taking’ attitude.

2. What sequence should your story follow?
Be it work experience or education, always tell the story from the current/ most recent to the first. NEVER write it the other way round.

3. Does your resume need to mention your marital status?
The new age resume does not require you to mention your marital status. However, if the job advertisement clearly states this as a requirement, do fulfil it. Quick Take

* Include a sharp Career Goal

* Choose the pdf format with discretion

* Fonts: Use Times New Roman, Calibri or Verdana

* Run a spell check

* Tweak to suit position and company of a potential employer

* Your latest work stint must appear first

* save the doc/pdf with meaning full name like : thanooj_j2ee_2.7yrs_25032011.

* writing a cover letter
Dear _______, I am applying for the role of ___________________ at your esteemed organisation _____________________.

4. How should you treat references?

Unless you have been specifically asked to provide references, it is acceptable to state in your covering letter/ email that you will provide references on request. Usually, two references are sufficient. Try to provide references from the two most recent phases of your career.
It is a good idea to inform the referees that you are giving out their contact information. It will also help if they know what kind of jobs you are applying for.

5. Should you send the resume as an MS Word document or a PDF?
Some organisations ask you to upload your resume. Usually they ask for an MS Word document. If you are mailing across your resume, you could choose either format.
A word of caution – do not get carried away if you decide to make it a PDF. Keep it simple – leave out visual histrionics. And whatever software you choose – send the resume in the most commonly used version.
The biggest advantage of using a pdf format is that it preserves the formatting irrespective of the version of the Acrobat Reader version or user settings.

6. Should you incorporate links in the resume?
If you are an engineer who writes a technical blog, go ahead and incorporate the link in your resume. If you are a website developer, the links to the pages created by you would certainly help.

Struts 2 Namespace configuration.

2011-03-22T00:10:00.000-07:00

*Struts 2 Namespace is a new concept to handle the multiple modules by given a namespace to each module. In addition, it can used to avoid conflicts between same action names located at different modules.
*Struts 2 Namespaces are the equivalent of Struts 1 multiple modules.

1. Namespace configuration
Let go through a Struts 2 namescape configuration example to know how it match with URL and folder.

P.S The package “name” will not affect the result, just give a meaningful name.

Struts 1.x – Multiple configuration files.

2011-03-21T23:35:00.000-07:00

1. Single module
A single module support multiple Struts configuration files.

In the web.xml, you can separate multiple Struts configure file by a comma “,“.

Test it:
1.http://localhost:8080/StrutsExample/Page1.do
It will display the page1.jsp
2.http://localhost:8080/StrutsExample/common/Welcome.do
It will display the page2.jsp
Both Struts configuration are loaded property.
--------------------------------------------------------
2. Multiple modules
Multiple modules, each has own Struts configuration files.

Both “struts-config-admin.xml” and “struts-config-admin.xml” files contains the same settings, Struts is able to differential it via the “config” parameter value in web.xml.

struts-config-admin.xml, struts-config-common.xml

web.xml

Test it
The “config/admin” will match to this URL pattern – http://localhost:8080/StrutsExample/admin/
The “config/common” will match to this URL pattern – http://localhost:8080/StrutsExample/common/

1.http://localhost:8080/StrutsExample/admin/Welcome.do
It will display the admin/welcome.jsp
2.http://localhost:8080/StrutsExample/common/Welcome.do
It will display the common/welcome.jsp
Each modules has own Struts configuration file.

Tomcat manager console

2011-02-02T21:47:00.000-08:00

we do discuss about tomcat manager console login :

we do for tomcat server installation, while installing it, i will ask us to give userName/password, though that we can access tomcat manager console.

where as, when we go for tomcat.zip, it won't ask for manager userName/pwd or so.
after unzipping tomcat.zip.
we need to set
JAVA_HOME=%{where our JAVA JDK s/w installed(reside)}%
CATALINA_HOME=%{where our Tomcat s/w unzip/installed(reside)}%
done.
now, when we try to access manager's console, then we need to edit %{CATALINA_HOME}%\conf\tomcat-users.xml

edit tomcat-users.xml :

if you already started tomcat server, shutdown server before edit

and save it.done.

now, run startup.bat
goto http://localhost:8080/
click on 'Tomcat Manager'
it will ask for userName/pwd, provide your specific details.

done.

Unit testing with JUnit and EasyMock

2011-01-16T22:28:00.000-08:00

What is a unit test?For the case of this tutorial, we'll define a unit test as a test of a single isolated component in a repeatable way. Let's go thru that one section at a time to get a clearer idea of what goes into a unit test.
"a test". This means to verify something is correct. In order for us to have a valid unit test, we need to actually validate that after a start condition A, an end condition B exists. "...a single isolated component...". This is what separates a unit test from other types of tests. In order for it to be a unit test, it must test something in isolation, aka without dependencies. The reason for this is that we are testing the component itself and not it's interaction with other components (that is an integration test). Finally, although most definitions don't include this piece, "...in a repeatable way" is a very important piece of the definition. It's one thing to run a test that passes. It's quite different to have something you can run in a repeatable manor at any point to see if changes you made effected how the component behaves. For example, if you choose to do some refactoring to improve performance, can you rerun your unit test to verify that you didn't change the behavior of the component.
Setup
I will be using Eclipse 3.3 Europa to do this tutorial. To begin, create a new java project and call it JUnitTutorial. Right click on your new project and select New --> Folder. Name it lib and click Finish. Usually you don't want to package your test code with your regular code, so let's make an additional source directory, test. To do that, right click on your new project and select Properties. Select Java Build Path from the available options. In the Java Build Path window, click Add Folder. From the Add Folder dialog, select Create New Folder, name it test and click Finish. Next we need to add JUnit to our build path. Since it comes with Eclipse, all we need to do is to go to the Libraries tab, click the button Add Library, select JUnit and click Next. Select JUnit 4 and click Finish. Click ok to exit the Preferences window. We will also need to download and add the EasyMock jar files to our project. You can find the jars here. Once you download the zip file (we are using version 2.3 for this tutorial), extract the easymock.jar file and place it in the lib folder you created earlier. In Eclipse, right click on your project and select Properties. On the menu to the left, click Java Build Path and select the Libraries tab. Click the button Add Jar on the right. In the window that pops up, add the easymock.jar and click Ok. Click Ok to close the Properties window. You should now be ready to start your development.
The requirementsIn test driven design, we develop the unit test before the functionality. We write a test that verifies that the class should do X after our call. We prove that the test fails, we then create the component to make the test pass. In this case, we are going to create a service with a method that authenticates a user. Below is a class diagram of the scenario.

The interfacesWe will start our coding by defining two interfaces, LoginService and UserDAO We will implement LoginService, however since in this tutorial UserDAO will be mocked, we won't bother implementing it right now. For LoginService, we have a single method that takes a String userName and String password and returns a boolean (true if the user was found, false if it was not). The interface looks like this:

/**
* Provides authenticated related processing.
*/
public interface LoginService {

/**
* Handles a request to login. Passwords are stored as an MD5 Hash in
* this system. The login service creates a hash based on the paramters
* received and looks up the user. If a user with the same userName and
* password hash are found, true is returned, else false is returned.
*
* @parameter userName
* @parameter password
* @return boolean
*/
boolean login(String userName, String password);
}
The UserDAO interface will look very similar to the LoginService. It will have a single method that takes a userName and hash. The hash is an MD5 hashed version of the password, provided by the above service.

/**
* Provides database access for login related functions
*/
public interface UserDAO {

/**
* Loads a User object for the record that
* is returned with the same userName and password.
*
* @parameter userName
* @parameter password
* @return User
*/
User loadByUsernameAndPassword(String userName, String password);
}
The test caseBefore we begin development, we will develop our test. Tests are structured by grouping methods that perform a test together in a test case. A test case is a class that extends junit.framework.TestCase. So in this case, we will begin by developing the test case for LoginService. To start, in your test directory, create a new class named LoginServiceTest and make it extend junit.framework.TestCase.

The lifecycle of a test execution consists of three main methods:
public void setUp()setUp is executed before each of the test. It is used to perform any setup required before the execution of your test. Your implementation will override the default empty implementation in TestCase.
public void testSomething()testSomething is the actual test method. You may have many of these within a single test case. Each one will be executed by your test runner and all errors will be reported at the end.
public void tearDown()tearDown is executed after each test method. It is used to perform any cleanup required after your tests.

So to begin flushing out our test case, we'll start with the setUp method. In this method, we'll instantiate an instance of the service to be tested. We'll also create our first mock object, UserDAO. You can see the source of our test below.

import junit.framework.TestCase;
import static org.easymock.EasyMock.createStrictMock;
import static org.easymock.EasyMock.expect;
import static org.easymock.EasyMock.replay;
import static org.easymock.EasyMock.verify;
import static org.easymock.EasyMock.eq;
/**
* Test case for LoginService.
*/
public class LoginServiceTest extends TestCase{

private LoginServiceImpl service;
private UserDAO mockDao;

/**
* setUp overrides the default, empty implementation provided by
* JUnit's TestCase. We will use it to instantiate our required
* objects so that we get a clean copy for each test.
*/
@Override
public void setUp() {
service = new LoginServiceImpl();
mockDao = createStrictMock(UserDAO.class);
service.setUserDAO(mockDao);
}
}
EasyMock works by implementing the proxy pattern. When you create a mock object, it creates a proxy object that takes the place of the real object. The proxy object gets it's definition from the interface you pass when creating the mock. We will define what methods are called and their returns from within our test method itself.

When creating a mock object, there are two types, a mock and a strict mock. In either case, our test will tell the mock object what method calls to expect and what to return when they occur. A basic mock will not care about the order of the execution of the methods. A strict mock, on the other hand, is order specific. Your test will fail if the methods are executed out of order on a strict mock. In this example, we will be using a strict mock.

The next step is to create our actual test method (for reference, we will not be implementing a tearDown method for this test case, it won't be needed in this example). In our test method, we want to test the following scenario:

Even with the very basic method we want to test above, there are still a number of different scenarios that require tests. We will start with the "rosy" scenario, passing in two values and getting a user object back. Below is the source of what will be our new test method.

...
/**
* This method will test the "rosy" scenario of passing a valid
* username and password and retrieveing the user. Once the user
* is returned to the service, the service will return true to
* the caller.
*/
public void testRosyScenario() {
User results = new User();
String userName = "testUserName";
String password = "testPassword";
String passwordHash =
"�Ӷ & I7��Ni=.";
expect(mockDao.loadByUsernameAndPassword(eq(userName), eq(passwordHash)))
.andReturn(results);

replay(mockDao);
assertTrue(service.login(userName, password));
verify(mockDao);
}
...
So let's go thru the code above. First, we create the expected result of our DAO call, results. In this case, our method will just check to see if an object was returned, so we don't need to populate our user object with anything, we just need an empty instance. Next we declare the values we will be passing into our service call. The password hash may catch you off guard. It's considered unsafe to store passwords as plain text so our service will generate an MD5 hash of the password and that value is the value that we will pass to our DAO.

The next line is a very important line in our test that alot happens, so let's walk thru it step by step:

expect(mockDao.loadByUsernameAndPassword()This is a call to the static method EasyMock.expect. It tells your mock object to expect the method loadByUsernameAndPassword to be called.
eq(userName), eq(passwordHash)
This code isn't always needed. When EasyMock compares the values passed to the method call, it does and == comparison. Because we are going to create the MD5 hash within our method, an == check will fail, so we have to use one of EasyMock's comparators instead. The eq comparator in this case will compare the contents of the string using it's .equals method. If we were not doing the MD5 hash, this line would be expect(mockDao.loadByUsernameAndPassword(userName, password).andReturn(results);
.andReturn(results);This tells our mock object what to return after this method is called.

The final three lines are the ones that do the testing work. replay(mockDao); tells EasyMock "We're done declaring our expectations. It's now time to run what we told you". assertTrue(service.login(userName, password)); does two things: executes the code to be tested and tests that the result is true. If it is false, the test will fail. Finally, verify(mockDao); tells EasyMock to validate that all of the expected method calls were executed and in the correct order.

So that's it for the test. Now all we have to do is write the code to make it pass. You can find that below.

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

public class LoginServiceImpl implements LoginService {

private UserDAO userDao;

public void setUserDAO(UserDAO userDao) {
this.userDao = userDao;
}

@Override
public boolean login(String userName, String password) {
boolean valid = false;
try {
String passwordHash = null;
MessageDigest md5 = MessageDigest.getInstance("MD5");
md5.update(password.getBytes());
passwordHash = new String(md5.digest());

User results =
userDao.loadByUsernameAndPassword(userName, passwordHash);
if(results != null) {
valid = true;
}
} catch (NoSuchAlgorithmException ignore) {}

return valid;
}
}
ConclusionSo that is it. I hope this gives you a more in depth view into JUnit and EasyMock. Unit testing is something that once you get used to it, makes you code better, provides you with a safety net for future refactoring and protects you from being burned by API changes. I strongly encourage that you give it a try. Until next time.

Static imports in java 1.5

2010-08-20T11:13:00.000-07:00

Static imports allow the static items of another class to be referenced without qualification. Used indiscriminately, this will likely make code more difficult to understand, not easier to understand.

Example

import java.util.*;
import static java.util.Collections.*;

public final class StaticImporter {

public static void main(String... aArgs){
List things = new ArrayList();
things.add("blah");

//This looks like a simple call of a method belonging to this class :
List syncThings = synchronizedList(things);

//However, it actually resolves to :
//List syncThings = Collections.synchronizedList(things);
}
}

An example in which a static import is likely acceptable is a constants class. For example, a scientific or engineering application might make wide use of Math.PI. A static import of java.lang.Math.* would allow a class to replace Math.PI with PI.

More generally, a business application might define a constants class, and import it statically. This would allow Consts.NEW_LINE to be referenced as NEW_LINE, for example.

by adding the word static after the import keyword, you change your import to a static one.when an import is static, all the accessible methods and variables of the class can be used without prefixing its access with the class name. For instance, if you static import the java.awt.Color class with import static java.awt.Color.*;, you just have to include RED in your code, instead of Color.RED.A simple version of this feature is as follows

import static java.awt.Color.*;
public class ImportTest {
public static void main(String args[]) {
System.out.println(RED);
}
}

servlet api source code download

2010-07-31T11:58:00.000-07:00

download

Thread - simple note

2010-07-31T11:12:00.001-07:00

Thread - a Breaf Note

Threads - Thread Synchronization

2010-07-31T10:59:00.001-07:00

* every instance of class Object and its subclass's has a lock
* primitive data type fields (Scalar fields) can only be locked via their enclosing class
* fields cannot be marked as synchronized however they can be declared volatile which orders the way they can be used or you can write synchronized accessor methods
* array objects can be synchronized BUT their elements cannot, nor can their elements be declared volatile
* Class instances are Objects and can be synchronized via static synchronized methods

Synchronized blocks

* allow you to execute synchronized code that locks an object without requiring you to invoke a synchronized method

synchronized( expr ) {
// 'expr' must evaluate to an Object
}

Synchronized methods

* declaring a method as synchronized ie synchronized void f() is equivalent to

void f() { synchronized(this) {
// body of method
}
}

* the synchronized keyword is NOT considered part of a method's signature. IT IS NOT AUTOMATICALLY INHERITED when subclasses override superclass methods
* methods in Interfaces CANNOT be declared synchronized
* constructors CANNOT be declared synchronized however they can contain synchronized blocks
* synchronized methods in subclasses use the same locks as their superclasses
* synchronization of an Inner Class is independent on it's outer class
* a non-static inner class method can lock it's containing class by using a synchronized block

synchronized(OuterClass.this) {
// body
}

Locking

* locking follows a built-in acquire-release protocol controlled by the synchronized keyword
* a lock is acquired on entry to a synchronized method or block and released on exit, even if the exit is the result of an exception
* you cannot forget to release a lock
* locks operate on a per thread basis, not on a per-invocation basis
* Java uses re-entrant locks ie a thread cannot lock on itself

class Reentrant {

public synchronized void a() {
b();
System.out.println("here I am, in a()");
}
public synchronized void b() {
System.out.println("here I am, in b()");
}
}

* in the above code, the synchronized method a(), when executed, obtains a lock on it's own object. It then calls synchronized method b() which also needs to acquire a lock on it's own object
* if Java did not allow a thread to reacquire it's own lock method b() would be unable to proceed until method a() completed and released the lock; and method a() would be unable to complete until method b() completed. Result: deadlock
* as Java does allow reentrant locks, the code compiles and runs without a problem

* the locking protocol is only followed for synchronized methods, it DOES NOT prevent unsynchronized methods from accessing the object
* once a thread releases a lock, another thread may acquire it BUT there is no guarantee as to WHICH thread will acquire the lock next

Class fields and methods

* locking an object does not automatically protect access to static fields
* protecting static fields requires a synchronized static block or method
* static synchronized statements obtain a lock on the Class vs an instance of the class
* a synchronized instance method can obtain a lock on the class

synchronized(ClassName.class) {
// body
}

* the static lock on a class is not related to any other class including it's superclasses
* a lock on a static method has no effect on any instances of that class (JPL pg 185)
* you cannot effectively protect static fields in a superclass by adding a new static synchronized method in a subclass; an explicit block synchronization is the preferred way
* nor should you use synchronized(getClass()); this locks the actual Class which might be different from the class in which the static fields are declared

Inner Classes in Java

2010-07-29T05:06:00.001-07:00

As we all know what an inner class is so lets try to know few more rules about Inner Classes.

Inner classes cannot have static members. only static final variables.

Interfaces are never inner.

Static classes are not inner classes.

Inner classes may inherit static members that are not compile-time constants even though they may not declare them.

Nested classes that are not inner classes may declare static members freely, in accordance with the usual rules of the Java programming language. Member interfaces are always implicitly static so they are never considered to be inner classes.A statement or expression occurs in a static context if and only if the innermost method, constructor, instance initializer, static initializer, field initializer, or explicit constructor invocation statement enclosing the statement or expression is a static method, a static initializer, the variable initializer of a static variable, or an explicit constructor invocation statement.

A blank final field of a lexically enclosing class may not be assigned within an inner class.

For Example:

class HasStatic {
static int j = 100;
}

class Outer{

final int z=10;

class Inner extends HasStatic {
static final int x = 3;
static int y = 4;
}

static class Inner2 {
public static int size=130;
}

interface InnerInteface {
public static int size=100;
}
}

public class InnerClassDemo {

public static void main(String[] args) {

Outer outer=new Outer();
System.out.println(outer.new Inner().y);
System.out.println(outer.new Inner().x);
System.out.println(outer.new Inner().j);

System.out.println(Outer.Inner2.size);

System.out.println(Outer.InnerInteface.size);
}
}

Hence it gives compilation problems as y cannot be used in inner class "Inner".

Also note Method parameter names may not be redeclared as local variables of the method, or as exception parameters of catch clauses in a try statement of the method or constructor. However, a parameter of a method or constructor may be shadowed anywhere inside a class declaration nested within that method or constructor. Such a nested class declaration could declare either a local class or an anonymous class.

For Example:
public class MethodParameterExamples {

public String s="bt";

public void m1(String s) {
s=this.s;
s="uk";

//abstract
class InnerClass extends MethodParameterExamples {

String s="ros";

public void m1() {
System.out.println(super.s=this.s);
}
}

InnerClass innerClass=new InnerClass();
innerClass.s=s;
innerClass.m1();

}

public static void main(String[] args) {

MethodParameterExamples methodParameterExamples=new MethodParameterExamples();
methodParameterExamples.m1("vij");
System.out.println(methodParameterExamples.s);

}

}

Hence Prints the output:
uk
bt

Now coming to Section Nested Inner Classes:

Consider the below program.

class WithDeepNesting {
boolean toBe;

WithDeepNesting(boolean b) { toBe = b;}

class Nested {
boolean theQuestion;

class DeeplyNested {

DeeplyNested(){
theQuestion = toBe || !toBe;
}
}
}

public static void main(String[] args) {

WithDeepNesting withDeepNesting=new WithDeepNesting(true);
WithDeepNesting.Nested nested=withDeepNesting.new Nested();
nested.new DeeplyNested();
System.out.println(nested.theQuestion);

}
}

Please note that Inner classes whose declarations do not occur in a static context may freely refer to the instance variables of their enclosing class. An instance variable is always defined with respect to an instance. In the case of instance variables of an enclosing class, the instance variable must be defined with respect to an enclosing instance of that class. So, for example, the class Local above has an enclosing instance of class Outer. As a further example:

Here, every instance of WithDeepNesting.Nested.DeeplyNested has an enclosing instance of class WithDeepNesting.Nested (its immediately enclosing instance) and an enclosing instance of class WithDeepNesting (its 2nd lexically enclosing instance). Hence it prints: true.

Serialization Interview Questions

2010-07-28T22:37:00.000-07:00

Q1) What is Serialization?

Ans) Serializable is a marker interface. When an object has to be transferred over a network ( typically through rmi or EJB) or persist the state of an object to a file, the object Class needs to implement Serializable interface. Implementing this interface will allow the object converted into bytestream and transfer over a network.

Q2) What is use of serialVersionUID?

Ans) During object serialization, the default Java serialization mechanism writes the metadata about the object, which includes the class name, field names and types, and superclass. This class definition is stored as a part of the serialized object. This stored metadata enables the deserialization process to reconstitute the objects and map the stream data into the class attributes with the appropriate type
Everytime an object is serialized the java serialization mechanism automatically computes a hash value. ObjectStreamClass's computeSerialVersionUID() method passes the class name, sorted member names, modifiers, and interfaces to the secure hash algorithm (SHA), which returns a hash value.The serialVersionUID is also called suid.
So when the serilaize object is retrieved , the JVM first evaluates the suid of the serialized class and compares the suid value with the one of the object. If the suid values match then the object is said to be compatible with the class and hence it is de-serialized. If not InvalidClassException exception is thrown.

Changes to a serializable class can be compatible or incompatible. Following is the list of changes which are compatible:

* Add fields
* Change a field from static to non-static
* Change a field from transient to non-transient
* Add classes to the object tree

List of incompatible changes:

* Delete fields
* Change class hierarchy
* Change non-static to static
* Change non-transient to transient
* Change type of a primitive field

So, if no suid is present , inspite of making compatible changes, jvm generates new suid thus resulting in an exception if prior release version object is used .
The only way to get rid of the exception is to recompile and deploy the application again.

If we explicitly metion the suid using the statement:

private final static long serialVersionUID =

then if any of the metioned compatible changes are made the class need not to be recompiled. But for incompatible changes there is no other way than to compile again.

Q3) What is the need of Serialization?

Ans) The serialization is used :-

* To send state of one or more object’s state over the network through a socket.
* To save the state of an object in a file.
* An object’s state needs to be manipulated as a stream of bytes.

Q4) Other than Serialization what are the different approach to make object Serializable?

Ans) Besides the Serializable interface, at least three alternate approaches can serialize Java objects:

1)For object serialization, instead of implementing the Serializable interface, a developer can implement the Externalizable interface, which extends Serializable. By implementing Externalizable, a developer is responsible for implementing the writeExternal() and readExternal() methods. As a result, a developer has sole control over reading and writing the serialized objects.
2)XML serialization is an often-used approach for data interchange. This approach lags runtime performance when compared with Java serialization, both in terms of the size of the object and the processing time. With a speedier XML parser, the performance gap with respect to the processing time narrows. Nonetheless, XML serialization provides a more malleable solution when faced with changes in the serializable object.
3)Finally, consider a "roll-your-own" serialization approach. You can write an object's content directly via either the ObjectOutputStream or the DataOutputStream. While this approach is more involved in its initial implementation, it offers the greatest flexibility and extensibility. In addition, this approach provides a performance advantage over Java serialization.

Q5) Do we need to implement any method of Serializable interface to make an object serializable?

Ans) No. Serializable is a Marker Interface. It does not have any methods.

Q6) What happens if the object to be serialized includes the references to other serializable objects?

Ans) If the object to be serialized includes the references to other objects whose class implements serializable then all those object’s state also will be saved as the part of the serialized state of the object in question. The whole object graph of the object to be serialized will be saved during serialization automatically provided all the objects included in the object’s graph are serializable.

Q7) What happens if an object is serializable but it includes a reference to a non-serializable object?

Ans- If you try to serialize an object of a class which implements serializable, but the object includes a reference to an non-serializable class then a ‘NotSerializableException’ will be thrown at runtime.

e.g.

public class NonSerial {
//This is a non-serializable class
}

public class MyClass implements Serializable{
private static final long serialVersionUID = 1L;
private NonSerial nonSerial;
MyClass(NonSerial nonSerial){
this.nonSerial = nonSerial;
}
public static void main(String [] args) {
NonSerial nonSer = new NonSerial();
MyClass c = new MyClass(nonSer);
try {
FileOutputStream fs = new FileOutputStream("test1.ser");
ObjectOutputStream os = new ObjectOutputStream(fs);
os.writeObject(c);
os.close();
} catch (Exception e) { e.printStackTrace(); }
try {
FileInputStream fis = new FileInputStream("test1.ser");
ObjectInputStream ois = new ObjectInputStream(fis);
c = (MyClass) ois.readObject();
ois.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}

On execution of above code following exception will be thrown –
java.io.NotSerializableException: NonSerial
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java)

Q8) Are the static variables saved as the part of serialization?

Ans) No. The static variables belong to the class and not to an object they are not the part of the state of the object so they are not saved as the part of serialized object.

Q9) What is a transient variable?

Ans) These variables are not included in the process of serialization and are not the part of the object’s serialized state.

Q10) What will be the value of transient variable after de-serialization?

Ans) It’s default value.
e.g. if the transient variable in question is an int, it’s value after deserialization will be zero.

public class TestTransientVal implements Serializable{

private static final long serialVersionUID = -22L;
private String name;
transient private int age;
TestTransientVal(int age, String name) {
this.age = age;
this.name = name;
}

public static void main(String [] args) {
TestTransientVal c = new TestTransientVal(1,"ONE");
System.out.println("Before serialization: - " + c.name + " "+ c.age);
try {
FileOutputStream fs = new FileOutputStream("testTransients.ser");
ObjectOutputStream os = new ObjectOutputStream(fs);
os.writeObject(c);
os.close();
} catch (Exception e) { e.printStackTrace(); }

try {
FileInputStream fis = new FileInputStream("testTransients.ser");
ObjectInputStream ois = new ObjectInputStream(fis);
c = (TestTransientVal) ois.readObject();
ois.close();
} catch (Exception e) { e.printStackTrace(); }
System.out.println("After de-serialization:- " + c.name + " "+ c.age);
}

}

Result of executing above piece of code –
Before serialization: - Value of non-transient variable ONE Value of transient variable 1
After de-serialization:- Value of non-transient variable ONE Value of transient variable 0

Explanation –
The transient variable is not saved as the part of the state of the serailized variable, it’s value after de-serialization is it’s default value.

Q11) Does the order in which the value of the transient variables and the state of the object using the defaultWriteObject() method are saved during serialization matter?

Ans) Yes. As while restoring the object’s state the transient variables and the serializable variables that are stored must be restored in the same order in which they were saved.

Q12) How can one customize the Serialization process? or What is the purpose of implementing the writeObject() and readObject() method?

Ans) When you want to store the transient variables state as a part of the serialized object at the time of serialization the class must implement the following methods –
private void wrtiteObject(ObjectOutputStream outStream)
{
//code to save the transient variables state as a part of serialized object
}

private void readObject(ObjectInputStream inStream)
{
//code to read the transient variables state and assign it to the de-serialized object
}

e.g.

public class TestCustomizedSerialization implements Serializable{

private static final long serialVersionUID =-22L;
private String noOfSerVar;
transient private int noOfTranVar;

TestCustomizedSerialization(int noOfTranVar, String noOfSerVar) {
this.noOfTranVar = noOfTranVar;
this.noOfSerVar = noOfSerVar;
}

private void writeObject(ObjectOutputStream os) {

try {
os.defaultWriteObject();
os.writeInt(noOfTranVar);
} catch (Exception e) { e.printStackTrace(); }
}

private void readObject(ObjectInputStream is) {
try {
is.defaultReadObject();
int noOfTransients = (is.readInt());
} catch (Exception e) {
e.printStackTrace(); }
}

public int getNoOfTranVar() {
return noOfTranVar;
}

}

The value of transient variable ‘noOfTranVar’ is saved as part of the serialized object manually by implementing writeObject() and restored by implementing readObject().
The normal serializable variables are saved and restored by calling defaultWriteObject() and defaultReadObject()respectively. These methods perform the normal serialization and de-sirialization process for the object to be saved or restored respectively.

Q13) If a class is serializable but its superclass in not , what will be the state of the instance variables inherited from super class after deserialization?

Ans) The values of the instance variables inherited from superclass will be reset to the values they were given during the original construction of the object as the non-serializable super-class constructor will run.
E.g.

public class ParentNonSerializable {
int noOfWheels;

ParentNonSerializable(){
this.noOfWheels = 4;
}

}

public class ChildSerializable extends ParentNonSerializable implements Serializable {

private static final long serialVersionUID = 1L;
String color;

ChildSerializable() {
this.noOfWheels = 8;
this.color = "blue";
}
}

public class SubSerialSuperNotSerial {

public static void main(String [] args) {

ChildSerializable c = new ChildSerializable();
System.out.println("Before : - " + c.noOfWheels + " "+ c.color);
try {
FileOutputStream fs = new FileOutputStream("superNotSerail.ser");
ObjectOutputStream os = new ObjectOutputStream(fs);
os.writeObject(c);
os.close();
} catch (Exception e) { e.printStackTrace(); }

try {
FileInputStream fis = new FileInputStream("superNotSerail.ser");
ObjectInputStream ois = new ObjectInputStream(fis);
c = (ChildSerializable) ois.readObject();
ois.close();
} catch (Exception e) { e.printStackTrace(); }
System.out.println("After :- " + c.noOfWheels + " "+ c.color);
}

}

Result on executing above code –
Before : - 8 blue
After :- 4 blue

The instance variable ‘noOfWheels’ is inherited from superclass which is not serializable. Therefore while restoring it the non-serializable superclass constructor runs and its value is set to 8 and is not same as the value saved during serialization which is 4.

Q14) To serialize an array or a collection all the members of it must be serializable. True /False?

Ans) true.
-------------------------------------------------------
How many methods in the Serializable interface? Which methods of Serializable interface should I implement?

There is no method in the Serializable interface. It’s an empty interface which does not contain any methods. The Serializable interface acts as a marker, telling the object serialization tools that the class is serializable. So we do not implement any methods.

What is the difference between Serializalble and Externalizable interface? How can you control over the serialization process i.e. how can you customize the seralization process?

When you use Serializable interface, your class is serialized automatically by default. But you can override writeObject() and readObject() two methods to control more complex object serailization process. When you use Externalizable interface, you have a complete control over your class's serialization process. This interface contains two methods namely readExternal and writeExternal. You should implement these methods and write the logic for customizing the serialization process.

How to make a class or a bean serializable? How do I serialize an object to a file?

Or

What interface must an object implement before it can be written to a stream as an object?

An object must implement the Serializable or Externalizable interface before it can be written to a stream as an object. The class whose instances are to be serialized should implement an interface Serializable. Then you pass the instance to the ObjectOutputStream which is connected to a fileoutputstream. This will save the object to a file.

What happens to the object references included in the object?

The serialization mechanism generates an object graph for serialization. Thus it determines whether the included object references are serializable or not. This is a recursive process. Thus when an object is serialized, all the included objects are also serialized alongwith the original object.

What is serialization?

The serialization is a kind of mechanism that makes a class or a bean persistent by having its properties or fields and state information saved and restored to and from storage. That is, it is a mechanism with which you can save the state of an object by converting it to a byte stream.

Common Usage of serialization.

Whenever an object is to be sent over the network or saved in a file, objects are serialized.

What happens to the static fields of a class during serialization?

There are three exceptions in which serialization doesn’t necessarily read and write to the stream. These are
1. Serialization ignores static fields, because they are not part of any particular state.
2. Base class fields are only handled if the base class itself is serializable.
3. Transient fields.

What one should take care of while serializing the object?

One should make sure that all the included objects are also serializable. If any of the objects is not serializable then it throws a NotSerializableException.

What is a transient variable?

Or

Explain the usage of the keyword transient?

Or

What are Transient and Volatile Modifiers

A transient variable is a variable that may not be serialized i.e. the value of the variable can’t be written to the stream in a Serializable class. If you don't want some field to be serialized, you can mark that field transient or static. In such a case when the class is retrieved from the ObjectStream the value of the variable is null.

Volatile modifier applies to variables only and it tells the compiler that the variable modified by volatile can be changed unexpectedly by other parts of the program.

What is Serialization and deserialization?

Serialization is the process of writing the state of an object to a byte stream. Deserialization is the process of restoring these objects.

What is Externalizable?

Externalizable is an interface which contains two methods readExternal and writeExternal. These methods give you a control over the serialization mechanism. Thus if your class implements this interface, you can customize the serialization process by implementing these methods.

If you think that an important java interview question is missing or some answers are wrong in the site please contribute it to sriniappl@gmail.com

Debugging with Eclipse - artical

2010-07-21T22:42:00.001-07:00

http://www.vogella.de/articles/EclipseDebugging/article.html

The basics: override hashCode() and equals()

2010-07-20T13:02:00.000-07:00

If you want to override equals method in your class, you should also override hashCode method as well. There are a lot of ways the two methods can be implemented incorrectly.

I found the easiest way is to use the wizard in Eclipse, just running Source | Generate hashCode() and equals()... either from menu or context menu. For example, this is what Eclipse generated for a simple class Scrap with a instance variable number:

Correct Implementation Example

The following code exemplifies how all the requirements of equals and hashCode methods should be fulfilled so that the class behaves correctly and consistently with other Java classes. This class implements the equals method in such a way that it only provides equality comparison for the objects of the same class, similar to built-in Java classes like String and other wrapper classes.

package com;

class Test {
private int x;
private String y;
public Test(int x, String y) {

this.x = x;
this.y = y;
}
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + x;
result = prime * result + ((y == null) ? 0 : y.hashCode());
return result;
}
@Override
public boolean equals(Object obj) {
if (this == obj) {
return true;
}
if (obj == null) {
return false;
}
if (!(obj instanceof Test)) {
return false;
}
Test other = (Test) obj;
if (x != other.x) {
return false;
}
if (y == null) {
if (other.y != null) {
return false;
}
} else if (!y.equals(other.y)) {
return false;
}
return true;
}

}

public class HashCodeAndEquals {

/**
* @param args
*/
public static void main(String[] args) {

Test t = new Test(10,"rama");
Test t1 = new Test(10,"rama");
System.out.println(t==t1);
System.out.println(t.hashCode()==t1.hashCode());
System.out.println(t.equals(t1));
}
}
-------------------------------------------------------------
The theory (for the language lawyers and the mathematically inclined):

equals() (javadoc) must define an equality relation (it must be reflexive, symmetric, and transitive). In addition, it must be consistent (if the objects are not modified, then it must keep returning the same value). Furthermore, o.equals(null) must always return false.

hashCode() (javadoc) must also be consistent (if the object is not modified in terms of equals(), it must keep returning the same value).

The relation between the two methods is:

Whenever a.equals(b), then a.hashCode() must be same as b.hashCode().
In practice:

If you override one, then you should override the other.

Use the same set of fields that you use to compute equals() to compute hashCode().

Use the excellent helper classes EqualsBuilder and HashCodeBuilder from the Apache Commons Lang library. An example:

public class Person {
private String name;
private int age;
// ...

public int hashCode() {
return new HashCodeBuilder(17, 31). // two randomly chosen prime numbers
// if deriving: appendSuper(super.hashCode()).
append(name).
append(age).
toHashCode();
}

public boolean equals(Object obj) {
if (obj == null)
return false;
if (obj == this)
return true;
if (obj.getClass() != getClass())
return false;

Person rhs = (Person) obj;
return new EqualsBuilder().
// if deriving: appendSuper(super.equals(obj)).
append(name, rhs.name).
append(age, rhs.age).
isEquals();
}
}

Also remember:

When using a hash-based Collection or Map such as HashSet, LinkedHashSet, HashMap, Hashtable, or WeakHashMap, make sure that the hashCode() of the key objects that you put into the collection never changes while the object is in the collection. The bulletproof way to ensure this is to make your keys immutable, which has also other benefits

Struts Spring Plugin

2010-07-20T02:44:00.001-07:00

* Overview
* Features
* What's New
o Discontinued - April 12, 2004
o 0.1 - October 17, 2003
* Requirements
* Usage
* Contact

Overview

This project was originally created to integrate the Spring Framework's Inversion of Control (IoC) into Struts 1.1+. As of Spring's 1.0.1 release, the ContextLoaderPlugin was added to Spring that has this same functionality. Therefore, this project's plugin is no longer recommended for use. We continue to maintain this site for documentation and an example app.

The integration uses Spring to create and populate Struts actions, using IoC to resolve dependencies. It does NOT use a custom request processor and therefore can be more easily used with existing web applications and/or other Struts extensions.

To demonstrate the project, we modified the struts-example webapp that is distributed with Struts 1.1 to use Spring to resolve all UserDatabase dependencies automatically. Comments and suggestions are appreciated.
Features

* Intuitive Inversion of Control (IoC)
* Requires little or no direct references to Spring in the Struts webapp
* Can be used with other Struts extensions that use a custom RequestProcessor
* Can create new Actions for every request (aleviating need for thread-safe Actions)
* Includes modified Struts example

What's New
Discontinued - April 12, 2004

* This plugin is now part of Spring (as of 1.0.1). You can read more about Spring's Struts support on Matt Raible's Spring Live blog.

0.1 - October 17, 2003

* Initial release

Requirements

This plugin requires Struts 1.1 or greater.
Usage

To use the Struts Spring plugin, add the ContextLoaderPlugIn to your Struts config file (usually struts-config.xml):

The "contextConfigLocation" property is the location of the Spring beans configuration file.

For each action that uses Spring, you need to define the action mapping to use org.springframework.web.struts.DelegatingActionProxy and declare a matching (action "path" == bean "name") Spring bean for the actual Struts action. This is an example of an action that requires an instance of UserDatabase:

The corresponding Spring bean configuration:

For more information on the Spring configuration file format, see the Spring beans DTD.

The Struts action org.apache.struts.webapp.example.LogonAction will automatically receive a reference to UserDatabase without any work on its part or references to Spring by adding a standard JavaBean setter:

private UserDatabase database = null;

public void setUserDatabase(UserDatabase database) {
this.database = database;
}

hashCode() and equals()

2010-07-20T00:42:00.000-07:00

with out overriding of hashCode() method.

package com;

class Test{
String r;
Test(String r){
this.r =r;
}
}

public class TestHashCodeAndEquals {

private int no;
private String name;
public void setName(String name) {
this.name = name;
}

public String getName() {
return name;
}

public void setNo(int no) {
this.no = no;
}

public int getNo() {
return no;
}

public TestHashCodeAndEquals(int no,String name) {
this.setNo(no);
this.setName(name);

}

/*@Override
public int hashCode() {

return 11;
}*/

public static void main(String[] args) {

TestHashCodeAndEquals o1 = new TestHashCodeAndEquals(1,"rama");
System.out.println(o1.hashCode());
TestHashCodeAndEquals o2 = new TestHashCodeAndEquals(1,"rama");
System.out.println(o2.hashCode());
System.out.println(o1.equals(o2));
System.out.println((o1==o2)+" wew");

String s1 = "rama";
String s2 = "rama";
System.out.println(s1==s2);
System.out.println(s1.hashCode());
System.out.println(s2.hashCode());
String s11 = new String("rama");
String s21 = new String("rama");
System.out.println(s11==s21);
System.out.println(s11.equals(s21));
System.out.println(s11.hashCode());
System.out.println(s21.hashCode());
Integer i1 = new Integer(10);
Integer i2 = new Integer(1234);
System.out.println(i1==i2);
System.out.println(i1.equals(i2));
System.out.println(i1.hashCode());
System.out.println(i2.hashCode());
Test t1 = new Test("rama");
Test t2 = new Test("rama");
System.out.println(t1.equals(t2));
System.out.println(t1.hashCode());
System.out.println(t2.hashCode());

Thread t = new Thread();
Thread t11 = new Thread(t);
System.out.println(t.hashCode()+" "+t11.hashCode());

// other than System defined wapper classes, we will not get the hashcode equal if and only if we override the hashCode() method in our class.

// even though we override the hashCode() ,override the hashCode() in our class,we can have same hashcode for all instance ,still, equals() will return false

}
}
out put
.......
-1-
4072869
1671711
false
false wew
-2-
true
3492867
3492867
-3-
false
true
3492867
3492867
-4-
false
false
10
1234
-5-
false
4384790
9634993
-6-
1641745 11077203

------------------------------------------------------------------
with overriding of hashCode() method.
package com;

class Test{
String r;
Test(String r){
this.r =r;
}
}

public class TestHashCodeAndEquals {

private int no;
private String name;
public void setName(String name) {
this.name = name;
}

public String getName() {
return name;
}

public void setNo(int no) {
this.no = no;
}

public int getNo() {
return no;
}

public TestHashCodeAndEquals(int no,String name) {
this.setNo(no);
this.setName(name);

}

@Override
public int hashCode() {

return 11;
}

public static void main(String[] args) {

System.out.println("-1-");
TestHashCodeAndEquals o1 = new TestHashCodeAndEquals(1,"rama");
System.out.println(o1.hashCode());
TestHashCodeAndEquals o2 = new TestHashCodeAndEquals(1,"rama");
System.out.println(o2.hashCode());
System.out.println(o1.equals(o2));
System.out.println((o1==o2)+" wew");

String s1 = "rama";
String s2 = "rama";
System.out.println("-2-");
System.out.println(s1==s2);
System.out.println(s1.hashCode());
System.out.println(s2.hashCode());
System.out.println("-3-");
String s11 = new String("rama");
String s21 = new String("rama");
System.out.println(s11==s21);
System.out.println(s11.equals(s21));
System.out.println(s11.hashCode());
System.out.println(s21.hashCode());
System.out.println("-4-");
Integer i1 = new Integer(10);
Integer i2 = new Integer(1234);
System.out.println(i1==i2);
System.out.println(i1.equals(i2));
System.out.println(i1.hashCode());
System.out.println(i2.hashCode());
System.out.println("-5-");
Test t1 = new Test("rama");
Test t2 = new Test("rama");
System.out.println(t1.equals(t2));
System.out.println(t1.hashCode());
System.out.println(t2.hashCode());
System.out.println("-6-");
Thread t22 = new Thread();
Thread t11 = new Thread(t22);
System.out.println(t22.hashCode()+" "+t11.hashCode());

// other than System defined wapper classes, we will not get the hashcode equal if and only if we override the hashCode() method in our class.

// even though we override the hashCode() ,override the hashCode() in our class,we can have same hashcode for all instance ,still, equals() will return false

}
}
out put
.......
-1-
11
11
false
false wew
-2-
true
3492867
3492867
-3-
false
true
3492867
3492867
-4-
false
false
10
1234
-5-
false
1671711
11394033
-6-
4384790 9634993

The DROP TRIGGER statement

2010-07-19T23:02:00.001-07:00

In a DROP TRIGGER statement, the table name must be prepended to the name of the trigger:
DROP TRIGGER . mysql>
mysql>
mysql>
mysql> CREATE TABLE Employee(
-> id int,
-> first_name VARCHAR(15),
-> last_name VARCHAR(15),
-> start_date DATE,
-> end_date DATE,
-> salary FLOAT(8,2),
-> city VARCHAR(10),
-> description VARCHAR(15)
-> );
Query OK, 0 rows affected (0.03 sec)

mysql>
mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description)
-> values (1,'Jason', 'Martin', '19960725', '20060725', 1234.56, 'Toronto', 'Programmer');
Query OK, 1 row affected (0.00 sec)

mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description)
-> values(2,'Alison', 'Mathews', '19760321', '19860221', 6661.78, 'Vancouver','Tester');
Query OK, 1 row affected (0.00 sec)

mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description)
-> values(3,'James', 'Smith', '19781212', '19900315', 6544.78, 'Vancouver','Tester');
Query OK, 1 row affected (0.00 sec)

mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description)
-> values(4,'Celia', 'Rice', '19821024', '19990421', 2344.78, 'Vancouver','Manager');
Query OK, 1 row affected (0.00 sec)

mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description)
-> values(5,'Robert', 'Black', '19840115', '19980808', 2334.78, 'Vancouver','Tester');
Query OK, 1 row affected (0.00 sec)

mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description)
-> values(6,'Linda', 'Green', '19870730', '19960104', 4322.78,'New York', 'Tester');
Query OK, 1 row affected (0.00 sec)

mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description)
-> values(7,'David', 'Larry', '19901231', '19980212', 7897.78,'New York', 'Manager');
Query OK, 1 row affected (0.02 sec)

mysql>
mysql> insert into Employee(id,first_name, last_name, start_date, end_Date, salary, City, Description)
-> values(8,'James', 'Cat', '19960917', '20020415', 1232.78,'Vancouver', 'Tester');
Query OK, 1 row affected (0.00 sec)

mysql>
mysql> select * from Employee;
+------+------------+-----------+------------+------------+---------+-----------+-------------+
| id | first_name | last_name | start_date | end_date | salary | city | description |
+------+------------+-----------+------------+------------+---------+-----------+-------------+
| 1 | Jason | Martin | 1996-07-25 | 2006-07-25 | 1234.56 | Toronto | Programmer |
| 2 | Alison | Mathews | 1976-03-21 | 1986-02-21 | 6661.78 | Vancouver | Tester |
| 3 | James | Smith | 1978-12-12 | 1990-03-15 | 6544.78 | Vancouver | Tester |
| 4 | Celia | Rice | 1982-10-24 | 1999-04-21 | 2344.78 | Vancouver | Manager |
| 5 | Robert | Black | 1984-01-15 | 1998-08-08 | 2334.78 | Vancouver | Tester |
| 6 | Linda | Green | 1987-07-30 | 1996-01-04 | 4322.78 | New York | Tester |
| 7 | David | Larry | 1990-12-31 | 1998-02-12 | 7897.78 | New York | Manager |
| 8 | James | Cat | 1996-09-17 | 2002-04-15 | 1232.78 | Vancouver | Tester |
+------+------------+-----------+------------+------------+---------+-----------+-------------+
8 rows in set (0.00 sec)

mysql>
mysql>
mysql>
mysql> DELIMITER //
mysql>
mysql> CREATE TRIGGER myTrigger BEFORE UPDATE ON employee
-> FOR EACH ROW
-> BEGIN
->
-> IF NEW.id > 5 THEN
-> SET NEW.first_name = NEW.first_name+ " *";
-> END IF;
->
-> IF NEW.salary IS NULL OR NEW.salary = 0 THEN
-> SET NEW.salary = 100;
-> ELSE
-> SET NEW.salary = NEW.salary + 100;
-> END IF;
->
-> END
->
-> //
Query OK, 0 rows affected (0.02 sec)

mysql> DELIMITER ;
mysql>
mysql> SELECT * FROM INFORMATION_SCHEMA.TRIGGERS;
+-----------------+----------------+--------------+--------------------+----------------------+---------------------+--------------------+--------------+------------------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+--------------------+---------------+----------------------------+----------------------------+--------------------------+--------------------------+---------+----------+----------------+
| TRIGGER_CATALOG | TRIGGER_SCHEMA | TRIGGER_NAME | EVENT_MANIPULATION | EVENT_OBJECT_CATALOG | EVENT_OBJECT_SCHEMA | EVENT_OBJECT_TABLE | ACTION_ORDER | ACTION_CONDITION | ACTION_STATEMENT | ACTION_ORIENTATION | ACTION_TIMING | ACTION_REFERENCE_OLD_TABLE | ACTION_REFERENCE_NEW_TABLE | ACTION_REFERENCE_OLD_ROW | ACTION_REFERENCE_NEW_ROW | CREATED | SQL_MODE | DEFINER |
+-----------------+----------------+--------------+--------------------+----------------------+---------------------+--------------------+--------------+------------------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+--------------------+---------------+----------------------------+----------------------------+--------------------------+--------------------------+---------+----------+----------------+
| NULL | test | myTrigger | UPDATE | NULL | test | employee | 0 | NULL | BEGIN
IF NEW.id > 5 THEN
SET NEW.first_name = NEW.first_name+ " *";
END IF;
IF NEW.salary IS NULL OR NEW.salary = 0 THEN
SET NEW.salary = 100;
ELSE
SET NEW.salary = NEW.salary + 100;
END IF;
END | ROW | BEFORE | NULL | NULL | OLD | NEW | NULL | | root@localhost |
+-----------------+----------------+--------------+--------------------+----------------------+---------------------+--------------------+--------------+------------------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+--------------------+---------------+----------------------------+----------------------------+--------------------------+--------------------------+---------+----------+----------------+
1 row in set (0.03 sec)

mysql>
mysql>
mysql> DROP TRIGGER myTrigger;
Query OK, 0 rows affected (0.00 sec)

mysql>
mysql> SELECT * FROM INFORMATION_SCHEMA.TRIGGERS;
Empty set (0.02 sec)

mysql>
mysql>
mysql> drop table Employee;
Query OK, 0 rows affected (0.00 sec)

mysql>
mysql>

assertion replacing sop()s in code debugging from JDK 1.4

2010-07-19T05:36:00.000-07:00

Assertion in Java

Assertion facility is added in J2SE 1.4. In order to support this facility J2SE 1.4 added the keyword assert to the language, and AssertionError class. An assertion checks a boolean-typed expression that must be true during program runtime execution. The assertion facility can be enabled or disable at runtime.

Declaring Assertion

Assertion statements have two forms as given below

assert expression;

assert expression1 : expression2;

The first form is simple form of assertion, while second form takes another expression. In both of the form boolean expression represents condition that must be evaluate to true runtime.

If the condition evaluates to false and assertions are enabled, AssertionError will be thrown at runtime.

Some examples that use simple assertion form are as follows.

assert value > 5 ;

assert accontBalance > 0;

assert isStatusEnabled();

The expression that has to be asserted runtime must be boolean value. In third example isStatusEnabled() must return boolean value. If condition evaluates to true, execution continues normally, otherwise the AssertionError is thrown.

Following program uses simple form of assertion

//AssertionDemo.java

Class AssertionDemo{

Public static void main(String args[]){

System.out.println( withdrawMoney(1000,500) );

System.out.println( withdrawMoney(1000,2000) );

}

public double withdrawMoney(double balance , double amount){

assert balance >= amount;

return balance – amount;

}

}

In above given example, main method calls withdrawMoney method with balance and amount as arguments. The withdrawMoney method has a assert statement that checks whether the balance is grater than or equal to amount to be withdrawn. In first call the method will execute without any exception, but in second call it AssertionError is thrown if the assertion is enabled at runtime.

Enable/Disable Assertions

By default assertion are not enabled, but compiler complains if assert is used as an identifier or label. The following command will compile AssertionDemo with assertion enabled.

javac –source 1.4 AssertionDemo.java

The resulting AssertionDemo class file will contain assertion code.

By default assertion are disabled in Java runtime environment. The argument –eanbleassertion or –ea will enables assertion, while –disableassertion or –da will disable assertions at runtime.

The following command will run AssertionDemo with assertion enabled.

Java –ea AssertionDemo

or

Java –enableassertion AssertionDemo

Second form of Assertion

The second form of assertion takes another expression as an argument.

The syntax is,

assert expression1 : expression2;

where expression1 is the condition and must evaluate to true at runtime.

This statement is equivalent to

assert expression1 : throw new AssertionError(expression2);

Note: AssertionError is unchecked exception, because it is inherited from Error class.

Here, expression2 must evaluate to some value.

By default AssertionError doesn’t provide useful message so this form can be helpful to display some informative message to the user.
---------------------------------------------------------
links

http://download.oracle.com/docs/cd/E17476_01/javase/1.4.2/docs/guide/lang/assert.html

---------------------------------------------------------
1. How do I get the assert statement to work?
2. How do I get line numbers?
3. How do I get soft tabs?
4. How do I run Javadoc?
5. How do I see the javadoc for Sun-supplied classes?
6. Why are my JUnit results not showing up?
7. How do I create a test suite?
8. In JUnit, what's the difference between a "failure" and an "error"?
9. Why does Source->Format really mess up my formatting?
10. How do I import an existing program into Eclipse?

1. How do I get the assert statement to work?

In Eclipse 3.1, go to Window -> Preferences -> Java -> Compiler and set the Compiler Compliance Level to 1.4 or 5.0. Also check Use Default compliance settings. This tells the compiler to recognize and allow assert statements, but does not enable them.

In Eclipse 3.0 (Java 1.4), the settings are a little fussier. Go to Window -> Preferences -> Java -> Compiler -> Compliance and Classfiles and set:

Compiler Compliance Level: to 1.4
Use default compliance settings to unchecked
Generated .class files compatibility: to 1.4
Source compatibility: to 1.4
Disallow identifiers called 'assert': to Error
Compiler Compliance Level to 1.4

To enable (make active) assert statements, you must set a flag to the compiler. Go to Run -> Run... -> Arguments, and in the box labeled VM arguments:, enter either -enableassertions or just -ea. Accept the changes and close the dialog.

To get Javadoc to recognize the assert statement, see How do I run Javadoc?

2. How do I get line numbers?

Go to Window -> Preferences -> General -> Editors -> All Text Editors and check Show line numbers.

3. How do I get soft tabs?

To get soft tabs (tabs replaced by spaces) as you type, go to Window -> Preferences -> Java -> Code style-> Formatter and select the profile Java Conventions [built-in]. This should be set correctly to give soft tabs.

You can create your own profile by clicking Show...; for soft tabs, go to Indentation uncheck Use tab characters. After making your changes, you will be prompted for a name for your new profile.

4. How do I run Javadoc?

1. In the Package Explorer window, choose the package or file for which you want to generate documentation.
2. Choose File -> Export... -> Javadoc -> Next>
1. If the dialog box displays the message The Javadoc command does not exist, then you need to click the Configure... button and locate javadoc.exe. You already have this file--it is probably in YourJavaDirectory/jdk1.5.0/bin/.
3. Select the project, and the destination for the Javadoc files. Normally, you should only generate documentation for public fields and methods.
4. If you have no assert statements, you can click Finish at this point.
5. Click Next >.
6. Click Next > again.
7. Check JRE 1.4 source compatibility (otherwise your assert statements will be treated as errors). [See also How do I get the assert statement to work?]
8. Click Finish.

5. How do I see the javadoc for Sun-supplied classes?

If you hover (don't click) your mouse over the name of a method, you should see a simplified Javadoc explanation. If this doesn't work for Sun-supplied methods, then you don't have the source code installed. Here's how to install the source code:

1. Go to http://java.sun.com/j2se/1.5.0/download.jsp and choose to download the JDK 5.0 Source Code (I don't know what SCSL and JRL are, but SCSL worked for me).
2. For JDK 5.0, select Download(SCSL source) .
3. Register. This is relatively painless, especially if you either ignore or enjoy reading license agreements.
4. Download JDK (SCSL) 5.0 (1.5.0). This will give you a file jdk-1_5_0-src.scsl.zip. You do not need to unzip this file; Eclipse likes it the way it is.
5. In Eclipse, go to Projects -> Properties -> Java Build Path -> Libraries and expand JRE System Library [jre 1.5.0], then rt.jar. Select Source attachment and click Edit....
6. Select the above zip file.
7. Finish by exiting the dialog boxes.

6. Why are my JUnit results not showing up?

Maybe it's because all your tests succeeded. For more satisfying results, go to Window -> Preferences -> Java -> JUnit and uncheck Show the JUnit results view only when an error or failure occurs.

7. How do I create a test suite?

Go to File -> New -> Other... -> Java -> JUnit -> TestSuite, and click Next>. Select all the classes, and click Finish.

You can run this test suite the same way you run other JUnit tests.

8. In JUnit, what's the difference between a "failure" and an "error"?

A failure is when one of your assertions fails--that is, your program does something wrong, and your JUnit test notices and reports the fact. An error is when some other Exception occurs--one you haven't tested for and didn't expect, such as a NullPointerException or an ArrayIndexOutOfBoundsException.

9. Why does Source->Format really mess up my formatting?

You have unmatched brackets, braces, or parentheses, and the code reformatter is doing the best it can. Find the syntax error (somewhere near the beginning of the messed up formatting), fix it, and reformat.

10. How do I import an existing program into Eclipse?

Here are two ways that work. First,
1. In your workspace folder, create a new folder, and put your files into that folder.
2. Ask Eclipse to create a new project (File -> New -> Project...) and, for the name of the project, type in the exact name of your new folder.
3. Click Finish.
The second way is very similar:
1. Ask Eclipse to create a new project (File -> New -> Project...) with any suitable name.
2. Copy your files into the new folder.
3. In Eclipse's Package Explorer pane, right-click on the new project and choose Refresh from the pull-down menu.

---------------------------------------------------------

package com;

public class AssertTest {

/**
* @param args
*/

public boolean myErrorDisplay(){
System.out.println("here error");
return false;
}
public static void main(String[] args) {
// The following assert statement will stop execution
// with a message if assertions are turned on.

assert 1<10; assert true; assert 1>10 : new AssertTest().myErrorDisplay();
assert 1<10;
assert true;
// The following statement will only be printed if
// assertions are turned off because assertions
// were not allowed at run time by the -ea parameter.
System.out.println("Assertions are not active.");

}

}

Anonymous and Inner Class - example

2010-07-19T04:49:00.001-07:00

an example of a simple anonymous class

public class MainClass {
public static void main(String[] args) {
Ball b = new Ball() {
public void hit() {
System.out.println("You hit it!");
}
};
b.hit();
}

interface Ball {
void hit();
}
}

and

-------------------------------------------------------
package com;

public class AnuClass {

/**
* @param args
*/

public static void myanmethod(){

Ball b = new Ball(){
public void hit() {
System.out.println("You hit it!");
}
};
b.hit();
}

interface Ball {
void hit();
}

public static void main(String[] args) {
AnuClass.myanmethod();

}
}
-------------------------------------------------------

Access inner class from outside

public class Main {
public static void main(String[] args) {
Outer outer = new Outer();
outer.new Inner().hello();
}
}
class Outer {
public class Inner {
public void hello(){
System.out.println("Hello from Inner()");
}
}
}

------------------------------------------------------

Access inner class from outside

public class Main {
public static void main(String[] args) {
Outer outer = new Outer();
outer.new Inner().hello();
}
}
class Outer {
public class Inner {
public void hello(){
System.out.println("Hello from Inner()");
}
}
}

--------------------------------------------------------

package com;

public class InOutClass {

/**
* @param args
*/
public static void main(String[] args) {
Outer outer = new Outer();
outer.new Inner().hello();

new Thread(new Thread(){
int i=0;
public void run() {
try {
while (i<10) {
sleep(1000); System.out.print("1");
i++;
}
}
catch(InterruptedException ex) {}
}
}).start();

// second option

Thread t = new Thread(new Thread(){
public void run() {
int i=0;
try {
while (i<10) {
sleep(1000); System.out.print("2");
i++;
}
}
catch(InterruptedException ex) {}
}
});
t.start();

new Thread(new Runnable() {
public void run() {
int i=0;
while (i<10) { //sleep(1000); //sleep is not a method of Runnable Interface,its in Thread class
System.out.print("3");
}
}
}).start();

}

}

class Outer {
public class Inner {
public void hello(){
System.out.println("Hello from Inner()");
}
}
}