Pattern Design Basic Design Pattern 5

Question 1

The Visitor pattern is most useful when:

Accepted Answer

The object structure rarely changes but new operations are frequently added

Answer

Visitor lets you add new operations to an existing object hierarchy without modifying the classes, ideal when the structure is stable but operations evolve.

Question 2

What does 'programming to an interface, not an implementation' mean in the context of design patterns?

Accepted Answer

Depend on abstractions so implementations can be swapped without breaking clients

Answer

Depending on abstractions (interfaces or abstract classes) rather than concrete types makes code more flexible, extensible, and testable — a core GoF principle.

Question 3

Which pattern is used to interpret sentences in a language by representing its grammar as a class hierarchy?

Accepted Answer

Interpreter

Answer

The Interpreter pattern defines a grammar for a language and provides an interpreter to process sentences, with each grammar rule represented as a class.

Question 4

The Bridge pattern separates abstraction from implementation in order to:

Accepted Answer

Reduce the number of classes required by avoiding a Cartesian product explosion

Answer

Bridge prevents a proliferation of subclasses by letting abstraction and implementation vary independently rather than combining every permutation in a single class hierarchy.

Question 5

Favor composition over inheritance is a design principle. Which pattern most directly embodies this principle?

Accepted Answer

Strategy

Answer

Strategy composes an algorithm object into a context rather than inheriting behavior, making it a canonical example of preferring composition over inheritance.

Pattern Design Practice Test

Pattern Design Practice Test

Pattern Design Basic Design Pattern 5