This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
When you implement an interface you promise to provide the methods specified in the interface. The interface makes you do that much but the interface can't specify what you should do. So you'll make your method display() do whatever is right for you, and anybody who calls display() will have to live with the results.
Say you create a class that implements InterfaceA and InterfaceB. You could pass a single object instance to either of these methods and your object would do exactly the same thing both times.
So to your question "which does it override" the answer is none. It implements rather than overrides, and one implementation is good enough for both interfaces.
Hope that helps!
A good question is never answered. It is not a bolt to be tightened into place but a seed to be planted and to bear more seed toward the hope of greening the landscape of the idea. John Ciardi