Java enum : Creating an Enum

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/**
*
* @author thanooj
*/

enum OperatingSystems {windows, unix, linux, macintosh}


public class TestSampleEnum {

public static void main(String args[])
{
OperatingSystems os;

os = OperatingSystems.windows;
switch(os) {
case windows:
System.out.println("You chose Windows!");
break;
case unix:
System.out.println("You chose Unix!");
break;
case linux:
System.out.println("You chose Linux!");
break;
case macintosh:
System.out.println("You chose Macintosh!");
break;
default:
System.out.println("I don't know your OS.");
break;
}
}
}
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import java.io.IOException;
import java.io.PrintStream;

enum Grade { A, B, C, D, F, INCOMPLETE };

class Student {

private String firstName;
private String lastName;
private Grade grade;

public Student(String firstName, String lastName) {
this.firstName = firstName;
this.lastName = lastName;
}

public void setFirstName(String firstName) {
this.firstName = firstName;
}

public String getFirstName() {
return firstName;
}

public void setLastName(String lastName) {
this.lastName = lastName;
}

public String getLastName() {
return lastName;
}

public String getFullName() {
return new StringBuffer(firstName)
.append(" ")
.append(lastName)
.toString();
}

public void assignGrade(Grade grade) {
this.grade = grade;
}

public Grade getGrade() {
return grade;
}
}

public class TestEnum {

private Student student1, student2, student3;

public TestEnum() {
student1 = new Student("Brett", "McLaughlin");
student2 = new Student("Ben", "Rochester");
student3 = new Student("Dennis", "Erwin");
}

public void testGradeAssignment() throws IOException {
student1.assignGrade(Grade.B);
student2.assignGrade(Grade.INCOMPLETE);
student3.assignGrade(Grade.A);
}

public void listGradeValues(PrintStream out) throws IOException {
Grade[] gradeValues = Grade.values();

// for loop
for (int i=0; i out.println("Allowed value: '" + gradeValues[i] + "'");
}

// for/in loop
for (Grade g : gradeValues ) {
out.println("Allowed value: '" + g + "'");
}
}

public void testSwitchStatement(PrintStream out) throws IOException {
StringBuffer outputText = new StringBuffer(student1.getFullName());

switch (student1.getGrade()) {
case A:
outputText.append(" excelled with a grade of A");
break;
case B: // fall through to C
case C:
outputText.append(" passed with a grade of ")
.append(student1.getGrade().toString());
break;
case D: // fall through to F
case F:
outputText.append(" failed with a grade of ")
.append(student1.getGrade().toString());
break;
case INCOMPLETE:
outputText.append(" did not complete the class.");
break;
default:
outputText.append(" has a grade of ")
.append(student1.getGrade().toString());
break;
}

out.println(outputText.toString());
}

public static void main(String[] args) {
try {
TestEnum tester = new TestEnum();

tester.testGradeAssignment();
tester.listGradeValues(System.out);
tester.testSwitchStatement(System.out);
} catch (Exception e) {
e.printStackTrace();
}
}
}