CODEWITHSUNDEEP
javagenericsinterface
rajneesh2k10
rajneesh2k10

Reputation: 1590

Extend a generic interface and make it stricter in Java

TLDR: I want to make a generic interface definition stricter after extension.

Let's say we've operations and request/response objects on which they can operate.

I've defined a base interface which mandates every operation should have execute method in it.

public interface Operation<S, T> {
    T execute(S request);
}

I want to extend it to bunch of other interface which are for specific operations. e.g.

public interface ReadOperation<S extends ReadRequest, T extends ReadResponse> extends Operations {
    T execute(S readRequest);
}

Typically I would want to overwrite the base interface execute definition with a stricter definition in extending interface. But unfortunately it's not achievable as java adds an overloaded method with new execute definition.

I want to understand where does my intuition lack and how in some other form I can achieve it. Tell me if I'm doing it horribly wrong.

Closest I could find here: Overriding a method contract in an extended interface that uses generics (Java)?

Upvotes: 2

Views: 1603

Answers (1)

resueman
resueman

Reputation: 10613

The problem is because you're using a raw type. You don't provide a generic type to the extended Operation interface, so the compiler doesn't know that the S and T in each are meant to be the same. Change your ReadOperation to this:

public interface ReadOperation<S extends ReadRequest, T extends ReadResponse> extends Operation<S, T> {
    T execute(S readRequest);
}

Upvotes: 4

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