Computer Science: Design Patterns

What is the primary purpose of the Singleton design pattern?

The Singleton pattern ensures that a class has only one instance and provides a global point of access to that instance throughout the application.

Which design pattern defines a one-to-many dependency between objects so that when one object changes state, all its dependents are notified automatically?

The Observer pattern, often used in event-driven systems or the Model-View-Controller (MVC) architecture.

What structural pattern provides a simplified, high-level interface to a complex set of interfaces in a subsystem?

The Facade pattern, which hides the complexities of the system and provides an interface to the client that is easier to use.

Which creational pattern allows an object to be created by copying an existing instance rather than creating a new one from scratch?

The Prototype pattern, which uses a 'clone' method to duplicate objects, avoiding the overhead of standard construction.

What is the main goal of the Adapter pattern?

To allow classes with incompatible interfaces to work together by wrapping the original interface in a new interface that the client expects.

Which behavioral pattern provides a way to access the elements of an aggregate object sequentially without exposing its underlying representation?

The Iterator pattern, which abstracts the traversal logic away from the collection itself.

How does the Builder pattern differ from other creational patterns regarding the construction process?

It separates the construction of a complex object from its representation, allowing the same construction process to create different representations step-by-step.

In the Decorator pattern, how is behavior added to an object compared to traditional inheritance?

Behavior is added dynamically at runtime by wrapping the object in another class (the decorator), rather than statically through subclassing.

What is the primary difference between the Factory Method and the Abstract Factory pattern?

Factory Method uses inheritance to decide which object to instantiate (one product), while Abstract Factory uses composition to create families of related or dependent objects.

Which structural pattern uses a surrogate or placeholder for another object to control access to it?

The Proxy pattern, which can be used for lazy initialization, logging, access control, or remote service communication.