Re: Casting an object in equals Java 5

From:

Roland de Ruiter <roland.de.ruiter@example.invalid>

Newsgroups:

comp.lang.java.programmer

Date:

Tue, 30 Sep 2008 12:01:03 +0200

Message-ID:

<48e1f8df$0$192$e4fe514c@news.xs4all.nl>

On 30-9-2008 9:40, crazzybugger wrote:

Hi,
      I am stuck with a compiler warning while trying to cast an
object inside equals method.
Consider class A<I>{ }
inside this class, I am trying to override equals method. However, I
am not able to cast the received object into the proper type without
compiler warning.

Consider this implementation of equals
public boolean equals(Object that){
     if(that instanceof A){
         A<I> that1 = this.getClass().cast(that); // here I am
getting compiler warning.
        // perform comparisons...
    }
}

what is the right way to cast here ?
thank you...

if (that instanceof A) {
A<?> that1 = (A<?>)that;
...
}

The actual type parameter of "that" isn't known at runtime, so you can
only cast it safely to an A of unknown type, i.e. A<?>.

I wouldn't use getClass().cast() if A can have subclasses, let's say B
and C, because this cast will fail if "this" is an instance of B and
"that" is an instance of C.
--
Regards,

Roland