接口的默认实现？ 或保留为空

Question

So the question is not really easy to understand but I will try my best, lets say I have an interface :

interface OnWindowMoveListener{
    void onWindowMove(MotionEvent motionEvent);
}

Now in my class I have

OnWindowMoveListener onWindowMoveListener;

public void setOnWindowMoveListener(OnWindowMoveListener onWindowMoveListener){
    this.onWindowMoveListener = onWindowMoveListener;
}

Later in my code the onWindowMoveListener.onWindowMove() is called but I dont want to have to check if the onWindowMoveListener has been set by the user and thus not null, how would I create a default implementation for this listener ? Would I have to manually implement the interfaces in the main method of my class in case the user doesnt implement them himself or is there another way of doing this ? I have always been checking if the interface has been implemented before calling but want to know if there is a cleaner way of doing this. Thanks

Answer 1

Doing nullcheck is not a cost operation, but if you really need to avoid it, your best option would be to use the Null Object Design Pattern.

Create a implementation of your interface which does nothing, and than use it as default value of the onWindownMoveListener.

For more information about this design pattern, consult: https://sourcemaking.com/design_patterns/null_object/java-0