Comparing Objects for sort, Comparable Interface.

test.java

import java.io.*;
import java.util.*;

class A implements Comparable<A>
{
	private int data;
	public A(int data)
	{
		this.data = data;
	}
	@Override
	public int compareTo(A ob)
	{
		return ((Integer)this.data).compareTo(ob.data);
	}
	public int getData()
	{
		return(this.data);
	}
}	

public class test2
{
	public static void main(String[] args)
	{
		A ob1 = new A(5);
		A ob2 = new A(2);
		A ob3 = new A(1);
		List<A> newlist = new ArrayList<A>();
		newlist.add(ob1);
		newlist.add(ob2);
		newlist.add(ob3);
		System.out.println("Before Sorting");
		for(A elem: newlist)
		{
			System.out.print(elem.getData() + " ");
		}
		Collections.sort(newlist);
		System.out.println("After Sorting");
		for(A elem: newlist)
		{
			System.out.print(elem.getData() + " ");
		}
	}
}