Design Pattern Interview Questions

1. Explain the Flyweight, Builder, Mediator and Memento patterns.
2. Describe the decorator pattern and how it is used within the java.io package.

   Answer: Decorators are used to provide additional functionality to an object of some kind. The key to a decorator is that a decorator "wraps" the object decorated and looks to a client exactly the same as the object wrapped. This means that the decorator implements the same interface as the object it decorates. For example, a BufferedReader is just a decorator for a Reader.

3. Observer Pattern:
   • Draw the class diagram for the Observer Pattern.
   • What instance variables would you have in the Observable class?
   • What would happen if an Observer removes himself from the observers list when he is notified?
   • What is thread-safety and how can you make the Observer Pattern thread-safe?
4. Name your favourite design pattern.
5. Explain the Model-View-Controller (MVC) compound design pattern. What patterns is it composed of?

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