Confusion with templates, generics, and instanceof

From:
Greg Boettcher <WRITETOgregAT@gregboettcher.com>
Newsgroups:
comp.lang.java.programmer
Date:
Fri, 13 Mar 2009 15:45:15 -0700 (PDT)
Message-ID:
<33c4c79e-dca6-4451-87d9-986edd204a7b@z9g2000yqi.googlegroups.com>
I am still in my first year of learning Java, so by all means type
this up as a "newbie" question if you like.

I have started working with templates and generics. I don't fully
understand the underlying mechanics of them. Either because of that or
for whatever other reason, I have been having some problems.

I've tried to distill my problems down to an illustrative test case:

<code>

public class FooWrapper<T> {
    //-------------
    // Instance variable:
    private T foo;

    //-------------
    // Constructor:
    public FooWrapper(T foo) {
        this.foo = foo;
    }
    // Getter:
    public T getFoo() {
        return foo;
    }
}

</code>

The above code seems perfectly fine. However, suppose I try writing an
equals method. Two possibilities come to mind. The first looks like
this:

<code>

    public boolean equals(Object o) {
        boolean result = false;
        if (o instanceof T) {
            T t = (T)(o);
            if (foo.equals(t.getFoo())) {
                result = true;
            }
        }
        return result;
    }

</code>

Basically this doesn't work because "o instanceof T" (where T is a
template) doesn't work.

The other possibility is:

<code>

    public boolean equals(T t) {
        boolean result = false;
        if (foo.equals(t.getFoo())) {
            result = true;
        }
        return result;
    }

</code>

I don't know why this doesn't work, but Eclipse says the following:

(1) "Name clash: The method equals(T) of type FooWrapper<T> has the
same erasure as equals(Object) of type Object but does not override
it"
(2) "The method getFoo() is undefined for the type T"

-----------------------

What in the heck is the solution here? Can anybody help?

Greg

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