Java: How do you access a parent class method two levels down?

Question

I have a class that extends a class that I need to overide, but I need to call that class's parent class. since I can't call super since that will execute the direct parent what is the best way to get the parent of my parent class?

I am sure this is a basic question, but its been a while since I have been doing any java.

class A
{
 public void myMethod()
 { /* ... */ }
}

class B extends A
{
 public void myMethod()
 { /* Another code */ }
}

class C extends B
{
 I need to call Class A here
 { /* Another code */ }
}

Answer 1

You don't: it violates encapsulation.

It's fine to say, "No, I don't want my own behaviour - I want my parent's behaviour" because it's assumed that you'll only do so when it maintains your own state correctly.

However, you can't bypass your parent's behaviour - that would stop it from enforcing its own consistency. If the parent class wants to allow you to call the grandparent method directly, it can expose that via a separate method... but that's up to the parent class.

Answer 2

You can't because it has been overridden by B. There is no instance of A inside C.

The thing is that you want to call a method of the class A, but from which instance? You have instantiated C, which is a class with a couple of own and inherited methods from B. If B is overriding a method of A, you can't access it from C, because the method itself belongs to C (is not a method of B, it has been inherited and now it's in C)

Possible workarounds:

B does not override myMethod()

C receives an instance of A and saves it as a class property.

myMethod() in A is static and you use A.myMethod() (I don't recommend it)

Answer 3

What you are asking is bad practice, What you are saying is that C is not a B, but an A. What you need to do is have C inherit from A. Then you can call super.

If not this is the only way...

public String A()
{
String s = "hello";
return s;
}

public String B()
{
String str = super.A();
return str;
}

public String C()
{
String s = super.B();
return s;
}

Answer 4

Besides what pakore answered, you could also chain super.myMethod() calls if that works for you. You will call myMethod() from A from the myMethod() in B.

class A {
   public void myMethod() {
     ....
   }
}

class B extends A {
   public void myMethod() {
     ....
     super.myMethod();
     ....
   }
}

class C extends B {
  public void myMethod() {
    ....
    super.myMethod(); //calls B who calls A
    ....
  }
}

You will eventually be calling myMethod from A, but indirectly... If that works for you.

Answer 5

You can't call A's method directly. In the few cases that I've hit this, the solution was to add a method in A to expose it's implementation. E.g.

class A
{
   public myMethod() {
        doAMyMethod();
   }

   void doAMyMethod() {
      // what A want's on doMyMethod, but now it's available
      // as a separately identifiable method
   }
}

class C extends B
{
   public void someStuff() {
      this.doAMyMethod();
   }
}

The scheme separates the public interface (doMyMethod) from the implementation (doAMyMethod). Inheritance does depend upon implementation details, and so this isn't strictly so bad, but I would try to avoid it if possible as it creates a tight coupling between the implementation in A and C.

Answer 6

What I do for this case is:

Make the object of class A inside the Class C and access the Class A there. This Example which clarifies more details:

class A{
int a;
}
class B extends A{
int a;
}
class C extends B{
int a; 
A obj = new A();
public void setData(int p,int q, int r) {

 this.a = p; //  points to it's own class
 super.a = q;// points to one up level class i.e in this case class B
 obj.a = r; // obj points the class A
}
 public void getData() {
    System.out.println("A class a: "+ obj.a);
    System.out.println("B class a: "+ super.a);
    System.out.println("C class a: "+this.a);
 }
}

public class MultiLevelInheritanceSuper {

 public static void main(String args[]){
    C2 obj = new C2();
    obj.setData(10, 20, 30);
    obj.getData();

 }

}

The output of this example is:

A class a: 30
B class a: 20
C class a: 10