Hashset size issue

Question

Here In below example i have created hashset in which i am adding three string values s1,s2,s3 though it shows me size of hashset 1. Why?

public static void main(String args[])
{
    String s1="abc";
    String s2=new String("abc");
    String s3="abc";
    Set setdemo=new HashSet();
    setdemo.add(s1);
    setdemo.add(s2);
    setdemo.add(s3);

    System.out.println("s1 hashcode -:"+ System.identityHashCode(s1));
    System.out.println("s2 hashcode -:"+ System.identityHashCode(s2));
    System.out.println("s3 hashcode -:"+ System.identityHashCode(s3));
    System.out.println("Set size is -:"+setdemo.size());
}

output:

s1 hashcode -:17523401
s2 hashcode -:8567361
s3 hashcode -:17523401
Set size is -:1

Answer 1

Set does not allow duplicates. As strings are put into a pool, they all point to the same instance.

Answer 2

Duplicate is identified as having an equivalent hash code, and returning true when tested for equality.

In your case, all the 3 Strings are identified as duplicates and since Set eliminates duplicates, the size is 1 in your case.