如何从不在Java的层次结构中的类调用抽象方法

Question

Below is my code. I have the abstract class Myabatract which has the method myMethod and I have a subclass MySubClass in which I have overridden the myMethod . In my client class I have a method callMethod from which I want to directly call the myMethod of Myabatract class is this possible?

abstract class Myabatract {

public void myMethod() {
    System.out.println("This is from Myabatract");
}

}

class MySubClass extends Myabatract  {
public void myMethod() {
    System.out.println("This is from MySubClass");
    super.myMethod();
}
}


class Client{
public void callMethod(){

}
}

Answer 1

You can create an anonymous implementation of the abstract class . This is particularly easy given the fact that it does not use any abstract methods.

class Client {
  public void callMethod() {
    Myabatract instance = new Myabatract() { /* nothing to implement*/ };

    instance.myMethod();
  }
}

As a user of the MySubClass type, you have no way to call the Myabatract method because it has been overridden, unless MySubClass were to expose it. Your only recourse would be to create another method that exposed the super method from within MySubClass (or other child implementations).

It's important to note that this will not work:

class Client {
  public void callMethod() {
    MySubClass instance = new MySubClass() {
      @Override
      public void myMethod() {
        super.myMethod();
      }
    };

    instance.myMethod();
  }
}

super is the non-anonymous class, MySubClass , which means nothing is actually changing. Interestingly, this can be worked around in C++ using the scope resolution operator ( :: ).

It's also worth pointing out that you are calling super.myMethod() in your implementation of MySubClass , which does invoke the Myabatract method.