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I want !instanceof

I'm about a year late for project coin. But I still want an obvious Java language feature: !instanceof. To illustrate:
  public void equals(Object other) {
    if (other !instanceof Foo) {
      return false;
    }
    return ((Foo) other).bar.equals(bar);
  }

With the instanceof operator, null instanceof T is false for all values of T. Symmetrically, I suppose null !instanceof T should always be true.

# posted by Jesse Wilson on Friday, March 05, 2010

Well, a little better than

if (!(other instanceof Foo))

# posted by Blogger Tetsuo on March 5, 2010 2:01 PM

Agreed. I've been using false == x instanceof Y to avoid the double parens.

# posted by Blogger Brian Harris on March 5, 2010 3:11 PM

I prefer the getClass() route for equals:
if (that != null || that.getClass() != getClass()) ...

In this context, instanceof violates the contract of equals, allowing a situation where a.equals(b) is true but b.equals(a) is false if b is an instance of a subclass and a an instance of the superclass.

# posted by Blogger Rory on March 5, 2010 3:46 PM

@Rory not true; List.equals() is only correct when implemented with instanceof.

# posted by Blogger swankjesse on March 5, 2010 4:47 PM

Damn where were you? I agree, this is annoying as hell.

# posted by Blogger Robert Konigsberg on March 5, 2010 6:39 PM

@swankjesse: That's because the contract for List#equals() is different to that for Object#equals() in such a way as to forbid subclasses from messing up symmetry the way they can for non-List Objects.

Still, I know there have been times when I've wanted to type !instanceof, whatever approach one usually favours for equals().

# posted by Blogger Rory on March 6, 2010 3:54 AM

I've always written (x instanceof String == false).

But then I never use ! to negate anyway, I think its much less readable than == false.

# posted by Blogger JodaStephen on March 9, 2010 1:33 PM

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