Re: Why use Objectg in Equals method?
pek wrote:
[...]
Another question I have is:
Why use Object as a parameter in the equals method?
Why don't just narrow it down as much as possible? If I have a Point
class, why not use public boolean equals(Point p); ? Not only will
this make the method easier to create, it will avoid comparing
superclasses (but not subclasses). After all, for most of the cases, I
will compare an object with another object of the same class anyway.
Of course, if you intend to compare with objects of different classes,
this would be irrelevant. But, how many times do you do that anyway?
How often do you use HashMaps? Or Sets?
It's quite common to write code that manipulates arbitrary
objects without knowing or caring exactly what class they belong
to, but nonetheless needs to ask "Are these two objects equal?"
Since the code knows only that the objects are Objects[*], it
needs to be able to call a method that answers the question "Is
this Object equal to that Object?"
[*] With generics, a class parameterized on <T> might know
that both objects are T's, and thus be able to call .equals(T).
But remember, generics are a late addition to Java. Also, they
are a compile-time phenomenon, and at run-time the T references
turn out to be just Object references.[**]
[**] I understand there's work afoot to "reify" generics,
but as far as I know it hasn't borne fruit yet.
--
Eric Sosman
esosman@ieee-dot-org.invalid