parent / child method overriding

Question

Consider the two below concrete classes:

public class A {
  protected void foo() {        
    System.out.println("A foo");
    bar();
  }

  protected void bar() {
    System.out.println("A bar");
  }
}

public class B extends A {
  @Override
  protected void foo() {
    super.foo();    
    System.out.println("B foo");
  }

  @Override
  protected void bar() {
    System.out.println("B bar");
  }
}


public class Test {

  public static void main(String[] args) {
    B b = new B();
    b.foo();
  }
}

The output will be:

A foo
B bar
B foo

Which is correct. But what if we need the result to be:

A foo
A bar
B foo

We have to override both methods.

Is there any solution for this in Java Object model?

Answer 1

Call a private internalBar() method from A.foo(), instead of calling the overridable bar(). The A.bar() method can also call internalBar() by default (to avoid code duplication), and still be overridden in subclasses.

Answer 2

You should use composition instead of inheritance. for example

public class Test {
    public static void main(String[] args) {
        B b = new B(new A());
        b.foo();
    }
}

class A implements Parent {
    public void foo() {
        System.out.println("A foo");
        bar();
    }

    public void bar() {
        System.out.println("A bar");
    }
}


interface Parent {
    void foo();
    void bar();
}

class B implements Parent {

Parent wrapped;

public B(Parent p) {
    this.wrapped = p;
}

@Override
public void foo() {
    wrapped.foo();
    System.out.println("B foo");
}

@Override
public void bar() {
    System.out.println("B bar");
}

}

Answer 3

If execution of bar() in class B is not a problem you can use super.bar() inside it.