Question

I’m a little bit new to objects in Java and I would appreciate some help. I hope I can explain my situation. I have a class, that I call GUI4EX, to handle the the programs GUI. In this class, I also have the main method that creates an instance of GUI4EX:

GUI4EX frame = new GUI4EX();

and also an instance of the class CustomHandler, but this is not done inside the main method:

CustomHandler customHandler = new CustomHandler();

From the code inside GUI4EX I call methods in customHandler like this: CustomHandler.getSomeValue(). How about if I want reach a method in GUI4EX from CustomHandler class? Is this possible and how would I do? Hope my qustions isn’t unclear! Thanks!

Answer 1

You have to understand one important thing for object-orientated programming: Methods belong to objects. You only* can call a method when you know an object whose method to call.

In your example, CustomHandler has to know the specific GUI4EX object to call a method on it. One possibility is to add a parameter to the constructor:

class CustomHandler {   
  private GUI4EX frame;

  public CustomHandler(GUI4EX theFrame) {
    frame = theFrame;
  }
}

Then you can access the field frame for calling a GUI method.

But note that you’re going to create a circular relationship. That means that both classes – CustomHandler and GUI4EX depend on each other. This may cause problems and result in bad code design. If you can, try avoiding such dependencies.

---

* There are also static methods, but they are used less frequently.