generics - Way to make Java parent class method return object of child class

Question

Is there any elegant way to make Java method located within parent class return object of child class, when this method is called from child class object?

I want to implement this without using additional interfaces and extra methods, and to use this without class casts, auxiliary arguments and so on.

Update:

Sorry that I was not so clear.

I want to implement method chaining, but I have problems with methods of parent class: I lose access to child class methods, when i call parent class methods... I suppose that I'v presented the core of my idea.

So the methods should return this object of this.getClass() class.

Answer 1

If you're just looking for method chaining against a defined subclass, then the following should work:

public class Parent<T> {

  public T example() {
    System.out.println(this.getClass().getCanonicalName());
    return (T)this;
  }
}

which could be abstract if you like, then some child objects that specify the generic return type (this means that you can't access childBMethod from ChildA):

public class ChildA extends Parent<ChildA> {

  public ChildA childAMethod() {
    System.out.println(this.getClass().getCanonicalName());
    return this;
  }
}

public class ChildB extends Parent<ChildB> {

  public ChildB childBMethod() {
    return this;
  }
}

and then you use it like this

public class Main {

  public static void main(String[] args) {
    ChildA childA = new ChildA();
    ChildB childB = new ChildB();

    childA.example().childAMethod().example();
    childB.example().childBMethod().example();
  }
}

the output will be

org.example.inheritance.ChildA 
org.example.inheritance.ChildA 
org.example.inheritance.ChildA 
org.example.inheritance.ChildB 
org.example.inheritance.ChildB