Which statement describes the Proxy pattern?

Which statement describes the Proxy pattern?

• A. It composes objects into tree structures to represent part-whole hierarchies.
• B. It acts as a stand-in to control access, defer expensive initialization, or add logging.
• C. It ensures a class has only one instance.
• D. It adds behavior to an object without altering its interface.

Answer: (B)

The Proxy pattern is about introducing a stand-in for another object to control access, delay expensive work, or add extra behavior around operations. A proxy sits in place of the real object and implements the same interface, so clients can use it transparently. This lets you defer creating the real object until it’s actually needed (lazy loading), enforce access control, or inject things like logging or caching without changing how the client talks to the object. The other descriptions point to different patterns: composing objects into trees for part-whole hierarchies is the Composite pattern; ensuring only one instance is the Singleton pattern; and adding behavior to an object without changing its interface is characteristic of the Decorator pattern. The Proxy’s key purpose is controlling access or deferring work, which is why this description is the best fit.

The Proxy pattern is about introducing a stand-in for another object to control access, delay expensive work, or add extra behavior around operations. A proxy sits in place of the real object and implements the same interface, so clients can use it transparently. This lets you defer creating the real object until it’s actually needed (lazy loading), enforce access control, or inject things like logging or caching without changing how the client talks to the object.

The other descriptions point to different patterns: composing objects into trees for part-whole hierarchies is the Composite pattern; ensuring only one instance is the Singleton pattern; and adding behavior to an object without changing its interface is characteristic of the Decorator pattern. The Proxy’s key purpose is controlling access or deferring work, which is why this description is the best fit.