Hiding methods from the GUI

Question

I am implementing the observer pattern in java to separate my model classes from the GUI. The problem is that, every time the update-method is called, the model-instance is given as a parameter. That means, the GUI can call methods on the model-objects which should not be called from the GUI. How to avoid that the GUI can manipulate the model objects?

Answer 1

In order to achieve that, you need to introduce another layer that will take a model object and convert it into DTO and return to GUI and vice versa. Kind of Data access design pattern used in many projects.

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Hope this gives you the idea.

Answer 2

• Create an Interface for the model class that only defines the methods that the GUI can call (ie a subset of the methods currently implemented by the model class that should only be seen by the GUI)
• Have the model class implement this new Interface, which should be trivial since the methods are already implemented there.
• In the methods where the model is passed, change the parameter type from the class of your model to the new interface that the model now implements