Re: Be Honest: Do you implement hashCode(), equals(), and toString() for every class you write?

From:
Patricia Shanahan <pats@acm.org>
Newsgroups:
comp.lang.java.programmer
Date:
Fri, 15 Sep 2006 13:18:40 GMT
Message-ID:
<QKxOg.12411$xQ1.8046@newsread3.news.pas.earthlink.net>
Chris Uppal wrote:

Mark Jeffcoat wrote:

Once you've put in your own equals() method, you really
need to override hashCode(), too. But pre-mature optimization
is evil, so here's the one I always use pre-profiling:

    public int hashCode() {
        return 0;
    }

I'm not kidding.


You should be.

/Anything/ would be better than that. Throw a runtime exception -- at least
that would guarantee that you weren't depending on having a working hashCode()
without realising it.


It is a functionally correct hashCode. If a and b reference equal
instances of the class, a.hashCode() is equal to b.hashCode(). If there
is any problem with it, it will show as poor hash structure performance.

I assume that if Mark found poor hash table performance during
profiling, he would upgrade the hashCode() method for the key class.

That said, when I'm writing an equals(), I know exactly which features
must be equal for two instances to be considered equal, which is the
only difficult part of writing a good hashCode(). I just write the two
methods together.

Patricia

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