Detailed usage of Comparable and Comparator

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.