Question

How to define a generic return type for an interface, so that it’s implementing class can have a return type of its own?

public interface A {
    public <T> T doSomething();     
}


public class ImplA implements A {
    public SomethingElseA doSomething() {
        return obj.doSomething();
    }
}

public class ImplB implements A {
    public SomethingElseB doSomething() {
        return obj.doSomething();
    }
}

Answer 1

Try something as follows.

interface A<T> {

  T doSomething();
}

class ImplA implements A<SomethingElseA> {

  public SomethingElseA doSomething() {
    ...
  }
}

class ImplB implements A<SomethingElseB> {

  public SomethingElseB doSomething() {
    ...
  }
}