Please explain the output

[indra negi]

Please explain the output that will be produced by the following code snippet:

import java.util.HashSet;

public class HashTest1 {
    
    private String str;
    
    public HashTest1(String str) {
        this.str = str;
    }
        
    @Override
    public int hashCode() {             
        return this.str.hashCode();
    }
    
    @Override
    public boolean equals(Object obj) { 
        return this.str.equals(obj);
    }
    
    public static void main(String args[]) {
        HashTest1 h1 = new HashTest1("1");
        HashTest1 h2 = new HashTest1("1");
        String s1 = new String("2");
        String s2 = new String("2");
        
        HashSet<Object> hs = new HashSet<Object>();
        hs.add(h1);
        hs.add(h2);
        hs.add(s1);
        hs.add(s2);
        
        System.out.print(hs.size());
    }
}    

[Ulf Dittmer]

What output does it produce? What in particular do you not understand about it?

[Harsh Pensi]

I think your doubt is why h1.equals(h2) is false.
Its because it is returning h1.str.equals(h2) and not h1.str.equals(h2.str).

[indra negi]

Hi,

The output produced was 3.

[Sean Clark]

Hey,

As harsh explained you have no implements your equals method correctly, so when it tests to see if the object is in the set then it get false because h1 doesn't equal h2.
Your s1 and s2 do equal therefore only 1 of them will be added.
So you end up with 3 elements in your set.

Sean

[Salil Vverma]

Hey Indra,
There would be three objects in the set h1,h2 and s1. h1 and h2 would not be equal reason being in the equals function it performs equals operation of string with HashTest object. In this comparision, it would always return false as they are different instance.
If you want h1 to be logically equal with h2 if they have the same string then you shall have to tweak the code a bit. You can see the example as mentioned below.It would give two objects in the set.

 
import java.util.HashSet;

public class HashTest1 {

	private final String str;

	public String getStr() {
		return str;
	}

	public HashTest1(String str) {
		this.str = str;
	}

	@Override
	public int hashCode() {
		return this.str.hashCode();
	}

	@Override
	public boolean equals(Object obj) {
		if (obj instanceof HashTest1) {
			HashTest1 ht = (HashTest1) obj;
			return this.str.equals(ht.getStr());
		} else
			return false;
	}

	public static void main(String args[]) {
		HashTest1 h1 = new HashTest1("1");
		HashTest1 h2 = new HashTest1("1");
		String s1 = new String("2");
		String s2 = new String("2");

		HashSet<Object> hs = new HashSet<Object>();
		hs.add(h1);
		hs.add(h2);
		hs.add(s1);
		hs.add(s2);
		System.out.print(hs.size());
	}
}
   

Regards
Salil Verma

[indra negi]

Great . Got it.

Thanks to all.