adding objects with same hashcodes and true value return by equals() method to a set.

[kamal krishna bhatt]

import java.util.HashSet;
import java.util.Set;
public class Test {
	public static void main(String[] args) {
		
		Set<abc> set=new HashSet<abc>();
		set.add(new abc());
		set.add(new abc());
		set.add(new abc());
		set.add(new abc());
		System.out.println(set);
	}
}
class abc{
	@Override
	public int hashCode() {
		// TODO Auto-generated method stub
		return 1;
	}
	@Override
	public boolean equals(Object obj) {
		// TODO Auto-generated method stub
		return true;
	}
}

when equals() returns false then output :
[abc@1, abc@1, abc@1, abc@1] no problem with that.

but when i run above code gives output:
abc@1
which means it is not going to add any duplicate object to set as a set checks for hashcode first then equals method to test two objects equality.
but does it really adds one object or it makes a linked list out of these all objects.

[Ganesh Gowtham]

public boolean add(E e) {
	return map.put(e, PRESENT)==null;
    }

check the return type which says whether it has added or not

Hope it helps

[Jesper de Jong]

Welcome to the Ranch.

A Set doesn't do anything with linked lists. When you put in four different objects that have the same hash code and for which equals() return true, then it will just store the last object that you put in, and it forgets about the previous objects. So no, it does not make a linked list out of the objects; it will just forget about the objects that you put in before.

[Ganesh Gowtham]

Jesper de Jong wrote:Welcome to the Ranch.

A Set doesn't do anything with linked lists. When you put in four different objects that have the same hash code and for which equals() return true, then it will just store the last object that you put in, and it forgets about the previous objects. So no, it does not make a linked list out of the objects; it will just forget about the objects that you put in before.

as said by Jong , it have recent object since it maintains Map

[kamal krishna bhatt]

thank you...................

[Mike Simmons]

Jesper de Jong wrote:A Set doesn't do anything with linked lists.

Well, a HashSet does use linked lists internally, to handle different objects that end up in the same hash bucket. Which is what is happening when you have equals() return false - the objects have the same hash code, so they end up in the same bucket, but since according to equals() they are all different objects, they all get separate entries in the HashSet, stored in a single bucket using a singly-linked list. When you change the code to make equals() return true, the linked list is unnecessary, because the objects all appear to be the same object. But the linked list is still part of the way HashSet is implemented internally.

[kamal krishna bhatt]

OK............