Pattern Design Behavioral Design Patterns 3

Question 1

Which behavioral pattern is best suited for implementing a redo/undo history with multiple levels?

Accepted Answer

Command + Memento

Answer

Command stores each operation as an executable/undoable object, while Memento captures state snapshots, together enabling full undo/redo history.

Question 2

The Template Method pattern uses ________ while the Strategy pattern uses ________.

Accepted Answer

Inheritance; composition

Answer

Template Method relies on subclasses overriding inherited steps (inheritance), while Strategy injects different algorithm objects (composition).

Question 3

In the Mediator pattern, a potential drawback is:

Accepted Answer

The mediator can become a God object that is too complex

Answer

Because all communication flows through it, the mediator can accumulate too much responsibility and become a maintenance bottleneck.

Question 4

The Visitor pattern's 'double dispatch' mechanism involves:

Accepted Answer

Calling accept() on the element which calls the visitor's method back

Answer

Double dispatch resolves the correct visitor method by first calling accept(visitor) on the element, which then calls the appropriate visit(element) on the visitor.

Question 5

Which pattern allows the same collection to be traversed with different algorithms without changing the collection?

Accepted Answer

Iterator

Answer

The Iterator pattern abstracts the traversal mechanism so different iterators (e.g., depth-first, breadth-first) can walk the same collection.

Pattern Design Practice Test

Pattern Design Practice Test

Pattern Design Behavioral Design Patterns 3