collections-------Set----------------TreeSet

import java.util.*;
class  TreeSetDemo
{
    public static void main(String[] args)
    {
        TreeSet ts=new TreeSet();
        ts.add(10);//doesn't follwo insertion order
        ts.add(20);
        ts.add(20);//don't allows duplicate values
        ts.add(30);
        ts.add(40);
        ts.add(50);
        ts.add(60);
        ts.add(70);

        System.out.println(ts.add(20));//false
        //System.out.println(ts.add(null));//allow one time get R.E. i.e. Exception in thread "main" java.lang.NullPointerExceptio
       

        //ts.add("a");//hetero geneous objects are allowed.
        //R.E. i.e. Exception in thread "main" java.lang.ClassCastException: java.lang.Integer canno
        //t be cast to java.lang.String
        //at java.lang.String.compareTo(Unknown Source)
        //at java.util.TreeMap.put(Unknown Source)
        //at java.util.TreeSet.add(Unknown Source)
       //at TreeSetDemo.main(TreeSetDemo.java:20)
       
        System.out.println(ts);
    }
}