Free Design Pattern Trivia Question and Answers

Question 1

Which Design Pattern should you employ when...
a class must only have one instance and be reachable by clients via a well-known access point?

Accepted Answer

Singleton

Answer

The Singleton design pattern ensures that a class has only one instance and provides a global point of access to that instance. This is essential when exactly one object is needed to coordinate actions across the system, such as a logger, configuration manager, or a database connection pool. It guarantees a single, consistent state for that specific resource.

Question 2

Which Design Pattern ought to be applied when a large number of related classes merely differ in behavior or when you require several algorithmic variations? You may specify algorithms that represent various space/time trade-offs, for instance.

Accepted Answer

Strategy

Answer

The Strategy design pattern defines a family of algorithms, encapsulates each one, and makes them interchangeable. It allows the algorithm to vary independently from clients that use it. This pattern is ideal when you have multiple ways to perform a specific task (e.g., different sorting algorithms or payment methods) and need to switch between them dynamically at runtime without altering client code.

Question 3

Which Design Pattern should you employ when...
there is a language to parse and abstract syntax trees can be used to express assertions in the language?

Accepted Answer

Interpreter

Answer

The Interpreter design pattern is used to define a grammatical representation for a language and provide an interpreter to deal with this grammar. It's particularly useful when you need to parse and evaluate expressions in a domain-specific language (DSL), where each rule in the grammar can be represented as a class, and an abstract syntax tree can be built to represent sentences in the language.

Question 4

Which Design Pattern ought to be applied when...
to manage extensions of subclasses. You can create a template method that only allows extensions at certain points and calls "hook" operations elsewhere.

Accepted Answer

Template Method

Answer

The Template Method pattern defines the skeleton of an algorithm in a base class, deferring some steps to subclasses. It allows subclasses to redefine certain parts of an algorithm without changing its overall structure. The 'hook' operations mentioned are specific points where subclasses can optionally extend or modify behavior.

Question 5

Which Design Pattern should you use when a system should be independent of the creation, composition, and representation of its products? Also, which Design Pattern should you use when the classes to instantiate are determined at runtime, such as when dynamic loading is used?

Accepted Answer

Prototype

Answer

The Prototype pattern creates new objects by copying an existing object, known as the prototype. This approach makes the system independent of how its products are created, composed, and represented. It's particularly useful when classes to instantiate are determined at runtime, as you can clone the appropriate prototype instance dynamically.

Pattern Design Practice Test

Pattern Design Practice Test

Free Design Pattern Trivia Question and Answers