how to use instanceof in generics

[tom chansky]

i realize there're some limitations in generics (J2SE 1.5); one of them is "naked" type parameter can't be used in instanceof operations.

for example:

class AClass<T> {

public void aMethod(Object arg) {
if(arg instanceof T) {} // Error

}
}

what if i need to check what class i'm dealing with? any ideas?

[Mogens Nidding]

As far as I know, there is no way to do what you want directly - no type parameters are present at runtime.

If you need to check, your best bet is to take a class literal as argument, for example to the constructor. As a trick, use T as type parameter for the class, like this:

class AClass<T> {
  Class<T> t;
 
  public <T> AClass(Class<T> t) {
    this.t = t;  // t is the concrete class represented by T
  }
 
  public void aMethod(Object arg) {
    if (arg == null || t.isInstance(arg));
  }
 
}

Hope this helps!