How to test instanceof on a generic class?

Question

I have an equals() method that contains this code:

if (other instanceof Peach<K, V>) {
    ...
}

However, this does not compile. How to fix this line of code?

Answer 1

As already pointed out, this is not possible. I would like to add that this is because of what is known as Type Erasure . The official Java tutorial has the following short summary:

Generics were introduced to the Java language to provide tighter type checks at compile time and to support generic programming. To implement generics, the Java compiler applies type erasure to:

• Replace all type parameters in generic types with their bounds or Object if the type parameters are unbounded. The produced bytecode, therefore, contains only ordinary classes, interfaces, and methods.
• Insert type casts if necessary to preserve type safety.
• Generate bridge methods to preserve polymorphism in extended generic types.

Type erasure ensures that no new classes are created for parameterized types; consequently, generics incur no runtime overhead.

The key here is "The produced bytecode, therefore, contains only ordinary classes, interfaces, and methods." . Because of this, it is not possible, to do the instanceof check you seek to do.

Answer 2

In short, you can't. Java erases generics types, so, at runtime, you don't have this information anymore.

You can use

if (other instanceof Peach) {
    ...
}