Re: do I need to override the equals() method?

From:

Lew <noone@lewscanon.com>

Newsgroups:

comp.lang.java.programmer

Date:

Sat, 04 Apr 2009 14:12:22 -0400

Message-ID:

<gr87u6$c1l$1@news.albasani.net>

Mike Schilling wrote:

Lew wrote:

NetBeans has this feature also. Alt-Insert, "equals() and
hashCode()", checkbox the desired fields, shows side by side the
checkboxes for each method so you can do what Mike likes.

For a class 'Foonteger' with a single 'BigInteger' field 'value'
(checkbox checked) it inserted:
--------------------------------
    @Override
    public boolean equals( Object obj )
    {
        if ( obj == null )
        {
            return false;
        }
        if ( getClass() != obj.getClass() )
        {
            return false;
        }
        final Foonteger other = (Foonteger) obj;
        if ( this.value != other.value &&
                (this.value == null || !this.value.equals(
        other.value )) ) {
            return false;
        }
        return true;
    }

    @Override
    public int hashCode()
    {
        int hash = 7;
        return hash;
    }
--------------------------------

Not my favorite implementation, but sufficient.

The hash is always 7? Yes, that doesn't break anything, but ...

Yeah, that bothers me, too.

IntelliJ (4.5, which is a bit long in the tooth) gives

    public boolean equals(Object o)
    {
        if (this == o) return true;
        if (!(o instanceof Foonteger)) return false;

        final Foonteger foonteger = (Foonteger) o;

        if (value != null ? !value.equals(foonteger.value) :
foonteger.value != null) return false;

        return true;
    }

    public int hashCode()
    {
        return (value != null ? value.hashCode() : 0);
    }

That is, IntelliJ gives a far better hash function, and the two
disagree about equals() appplied tio subclasses.

The trouble with applying 'equals()' to subclasses is that it breaks symmetry.

--
Lew