HashSet - Adding Integer values - Error Class Excpetion Help

Question

I am trying to add integers into the HashSet it is not allowing me to add it? does it mean that I cannot add integers. I also tried using the Integer class to input the values, still getting the same error. The Error is in the line : ts.add(3);
Any thoughts why such an error ?
The error that I get is :
java TreeTest
Exception in thread "main" java.lang.ClassCastException: java.lang.String
at java.lang.Integer.compareTo(Integer.java:35)
at java.util.TreeMap.compare(TreeMap.java:1093)
at java.util.TreeMap.put(TreeMap.java:465)
at java.util.TreeSet.add(TreeSet.java:210)
at TreeTest.main(TreeTest.java:12)
PK
import java.util.*;
class TreeTest
     public static void main(String[] args)
          TreeSet ts = new TreeSet();
          ts.add("Z");
          ts.add("A");
          ts.add("P");
          ts.add(3);
          ts.add(new Integer(1));
          ts.add(new Integer(7));
          System.out.println("The size is \t" + ts.size());
}

Answer 1

hii,
In the TreeSet the elements you add should be of same class type.
otherwise it can't do the sorting process.can u sort alphabets and numeric together? if u are adding Integer type only add int values or objs.if u want to add String add that n String objs.
try the following code
import java.util.*;
class TreeTest
     public static void main(String[] args)
          try
          TreeSet ts = new TreeSet();
          int a=3;
          //ts.add("Z");
          //ts.add("A");
          //ts.add("P");
          ts.add(new Integer(7));
          ts.add(new Integer(1));
          ts.add(a);
          System.out.println("The size is \t" + ts.size());     
          catch (Exception e)
               System.out.println(e);     
}