Problem in hashCode override (OCPJP forum at Coderanch)

Post by: Sidharth Khattri , Ranch Hand

Nov 11, 2013 08:53:54

This question is from scjptest.com

In the hashCode() override method, return again invokes hashCode() on this.str:
public int hashCode() {
return this.str.hashCode();
}

What does that mean and What will it return?
To see what will it return I added a print statement in hashCode in the above program:

And the output is:
49
49
2

I don't understand how hashCode returns 49 in the output. Can anyone please explain?

Post by: Matthew Brown , Bartender

Nov 11, 2013 09:39:52 (1 like)

It returns the hash code of the str member, which is a String. Have you checked the documentation for java.lang.String#hashCode()? That explains how it's calculated, which explains where the 49 comes from.

As for why it does that: remember that hashCode() needs to be consistent with equals(). The equals() method you've shown uses str to compare HashTest1 objects, so it makes perfect sense that hashCode() is based on str as well - it's the easiest way to make them consistent.

Post by: Sidharth Khattri , Ranch Hand

Nov 12, 2013 02:48:34

Matthew Brown wrote:It returns the hash code of the str member, which is a String. Have you checked the documentation for java.lang.String#hashCode()? That explains how it's calculated, which explains where the 49 comes from.

As for why it does that: remember that hashCode() needs to be consistent with equals(). The equals() method you've shown uses str to compare HashTest1 objects, so it makes perfect sense that hashCode() is based on str as well - it's the easiest way to make them consistent.

Thanks Matthew. I got it