CODEWITHSUNDEEP
javagenericsinheritance
Alpvax
Alpvax

Reputation: 172

Does something like a <getClass()> generic parameter exist in Java?

I would like to have an abstract method that has a parameter of the exact class of the instance. For example:

abstract class Foo {
    abstract void aFunc(???? newInst);
}
class Bar extends Foo {
    @Override
    void aFunc(Bar newInst);
}
class Baz extends Foo {
    @Override
    void aFunc(Baz newInst);
}

Effectively I would like to be able to access all subclass fields and methods without having to check and cast the newInst parameter. (As the function would be called from a central handler location that does the checks and casts).

I know I can do this by parameterising Foo with Foo<T extends Foo>, but I would ideally like to avoid declaring subclasses as class Name extends Foo<Name> if possible.

I doubt this is possible, and I have been unable to find anything on the topic, but I would just like to confirm that there is nothing i have missed.

Upvotes: 0

Views: 73

Answers (2)

nd.
nd.

Reputation: 8932

Meta-Comment:

the thing that you would like to have does break polymorphism: now you cannot use Bar or Baz everywhere you can use Foo because they have an aFunc signator that is not compatible anymore.

However, what you can do is have a return type that is more specific:

class Foo {
  Foo aFunc();
}

class Bar extends Foo {
  @Override
  Bar aFunc();
}

is valid. You can use an instance of Bar instead of Foo and call its aFunc method; then you can use the result of that method also as an instance of Foo. Therefore JLS allows for covariant return types since Java 1.5.

Upvotes: 2

Alpvax
Alpvax

Reputation: 172

Thanks to all who commented to help.

The correct way to do this is by declaring the class as class Bar extends Foo<Bar> and for the sake of simplicity, I will just pass Foo as the parameter and make all subclasses cast the argument themselves (if they need to).

Upvotes: 0

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