Java program to implement comparable interface ......

Here is the code ;-....

       

import java.util.*;
class Student implements Comparable {
 String firstname, lastname;
 int StudentId;
 double GPA;
 public Student() {
  System.out.println("this is the unparamaterized constructor");
 }

 public Student(String firstname, String lastname, int StudentId, double GPA) {
  if (firstname == null || lastname == null || StudentId == 0 || GPA == 0.0) {
   throw new IllegalArgumentException();
  }
  this.firstname = firstname;
  this.lastname = lastname;
  this.StudentId = StudentId;
  this.GPA = GPA;
 }

 public String firstname() {
  return firstname;
 }

 public String lastname() {
  return lastname;
 }

 public int StudentId() {
  return StudentId;
 }

 public double GPA() {
  return GPA;
 }

 public int compareTo(Object o) {
  double f = GPA - ((Student) o).GPA;

  if (f == 0.0) {
   return 0;
  } else if (f < 0.0)
   return -1;
  else
   return 1;
 }
}

public class ComparableTest extends Student {
 public static void main(String a[]) {
  TreeSet free = new TreeSet();
  free.add(new Student("gaurav", "yadav", 26, 4.0));
  free.add(new Student("paras", "yadav", 34, 3.0));
  free.add(new Student("suman", "yadav", 65, 9.0));
  free.add(new Student("ram", "saxena", 67, 7.8));
  free.add(new Student("nitasha", "kuntal", 74, 7.9));
  Object[] free2 = free.toArray();
  Student s;
  for (Object obj: free2) {
   s = (Student) obj;
   System.out.printf("name=%s %s id=%d GPA=%.1f\n", s.firstname(), s.lastname(), s.StudentId(), s.GPA());
  }
 }
}