Design Patterns

Which text below describes the Template Method pattern best?

• Encapsulates interchangeable behaviours and uses delegation to decide which one to use.
• Simplifies the interface of a group of classes.
• Subclasses decide how to implement steps in an algorithm.
• Changes the interface of one or more classes.
• Allows (a group of) objects to be notified when some state changes.

What is not a correct statement for the Hollywood Principle?

• High-level components control when and how low-level components participate in the computation.
• It is a way to prevent dependency rot.
• A low-level component never calls a high-level component directly.
• Call us, we don't call you.

Have a look at the class diagram for the Template Method pattern. What are the appropriate class names?

• 1. ConcreteClass 2. AbstractClass
• 1. AbstractClass 2. ConcreteClass

Which text below describes the Strategy Pattern best?

• Encapsulates interchangeable behaviours and uses delegation to decide which one to use.
• Simplifies the interface of a group of classes.
• Provides a way to traverse a collection of objects without exposing the collection's implementation.
• Changes the interface of one or more classes.
• Client treats collections of objects and individual objects uniformly.

Identify the aspects of your application that vary and separate them from what stays the same. What does that mean?

• Define a super class for what varies and let what stays the same extend that super class.
• Take what varies and "encapsulate" it so it won't affect the rest of the code.
• Put what varies and what stays the same together. Do it so that starting with an abstract class, all other classes inherit in a clever way.
• The number of classes should be identical with the number of interfaces.

What is a proper design principle?

• Use abstract classes to implement what varies.
• Put what varies and what stays the same together. Do ti so that starting with an abstract class, all other classes inherit in a clever way.
• Program to an interface, not an implementation.
• The number of classes should be identical with the number of interfaces.

Favour composition over inheritance. What does that mean?

• HAS-A can be better than IS-A.
• IS-A can be better than HAS-A.
• Do not use abstract classes.
• The number of classes should be identical with the number of interfaces.

Have a look at the class diagram for the Strategy pattern. What are the appropriate names for the classes?

• 1. Context 2. Strategy 3. ConcreteStrategyB 4. ConcreteStrategyA
• 1. Strategy 2. StrategyInterface 3. StrategyInterfaceImplA 4. StrategyInterfaceImplB

Have a look at the class diagram for the strategy pattern. What is the relation between class 1 and class 2 based on the methods and the previous question?

• Class 2 is-a class 1.
• Class 2 has-a class 1.
• Class 1 has-a class 2.
• Class 1 is-a class 2.

Which text below describes the Observer Pattern best?

• Allows (a group of) objects to be notified when some state changes.
• Provides a way to traverse a collection of objects without exposing the collection's implementation.
• Changes the interface of one or more classes.
• Simplifies the interface of a group of classes.
• Encapsulates interchangeable behaviours and uses delegation to decide which one to use.