is there some trick to share methods behavior while using encapsulation?

Question

I got this class structure:

abstract class A{
  protected void doTest(){};
  abstract void test();
}

abstract class B extends A{
}

class C extends B{
  public void test(){
    doTest();
  }
}

class D extends A{
  public void test(){
    doTest();
  }
}

D cannot extend B.
test() in both will implement the exact same functionality (that can contain several lines of code).
Currently I am being forced to copy the behavior identically.
I cannot create another class to implement the behavior because it access protected methods.

Is there any way out of this?

Answer 1

If test() truly is identical, it shouldn't be abstract.

abstract class A{
  protected void doTest(){};

  public void test() {
    //Shared functionality calling doTest() and doing other stuff. 
  }
}

Even if test() relies on fields in the various subclasses, you can make abstract getters and use those:

abstract class A{
  protected void doTest(){};

  protected abstract String getName();

  public void test() {
    //Shared functionality calling doTest() and doing other stuff. 
    //Can also use getName()
  }
}

abstract class B extends A {}

class C extends B {

    @Override public String getName() { return "C"; }

}

class D extends A {

    @Override public String getName() { return "D"; }

}