This might be a good candidate for the Decorator Pattern, which allows you to apply customized functionality to an individual object at run time. A good reference for this can be found on the Decorator Pattern Wikipedia page, which includes a detailed example of a Windowing system, with a UML class diagram for reference. A snippet of the code shows the decorator and the concrete decorator:
// abstract decorator class - note that it implements Window abstract class WindowDecorator implements Window { private final Window windowToBeDecorated; // the Window being decorated public WindowDecorator (Window windowToBeDecorated) { this.windowToBeDecorated = windowToBeDecorated; } @Override public void draw() { windowToBeDecorated.draw(); //Delegation } @Override public String getDescription() { return windowToBeDecorated.getDescription(); //Delegation } } // The first concrete decorator which adds vertical scrollbar functionality class VerticalScrollBarDecorator extends WindowDecorator { public VerticalScrollBarDecorator (Window windowToBeDecorated) { super(windowToBeDecorated); } @Override public void draw() { super.draw(); drawVerticalScrollBar(); } private void drawVerticalScrollBar() { // Draw the vertical scrollbar } @Override public String getDescription() { return super.getDescription() + ", including vertical scrollbars"; } }
In your case the decorator would be called DiggerDecorator and the concrete decorators could be called OverclockDecorator and RecoverDurabilityDecorator.
The code to instantiate a fully decorated object might look like this:
Digger decoratedDigger = new OverclockDecorator(new RecoverDurabilityDecorator(new SimpleDigger()));
As you can see, this solution still uses inheritance, but individual functionality can be "mixed in" as needed.
