Which statement best describes the Composite design pattern?

Which statement best describes the Composite design pattern?

• A. It composes objects into tree structures and treats leaves and composites uniformly through a common interface.
• B. It acts as a stand-in to control access, defer expensive initialization, or add logging.
• C. It provides a mechanism to select among multiple interchangeable algorithms at runtime.
• D. It encapsulates a request as an object to decouple the sender from the receiver.

Answer: (A)

The Composite pattern is about building tree-like structures of objects and treating individual items (leaves) and groups of items (composites) through the same interface. By defining a shared component interface, clients can perform operations on any node without needing to know whether it’s a single element or a container of elements. Composites implement ways to manage their children (add, remove, access) and propagate operations down the tree, while leaves implement the interface in a simpler way, often performing the operation directly with no child management. This uniform treatment makes it easy to compose complex structures like a file system (folders containing files and subfolders) or a scene graph in a UI, where operations such as render or print can be applied recursively. The other patterns described serve different intents: a stand-in pattern provides a proxy to control access or defer work; a strategy pattern selects among interchangeable algorithms at runtime; and a command pattern encapsulates a request as an object to decouple the sender from the receiver.

The Composite pattern is about building tree-like structures of objects and treating individual items (leaves) and groups of items (composites) through the same interface. By defining a shared component interface, clients can perform operations on any node without needing to know whether it’s a single element or a container of elements. Composites implement ways to manage their children (add, remove, access) and propagate operations down the tree, while leaves implement the interface in a simpler way, often performing the operation directly with no child management.

This uniform treatment makes it easy to compose complex structures like a file system (folders containing files and subfolders) or a scene graph in a UI, where operations such as render or print can be applied recursively.

The other patterns described serve different intents: a stand-in pattern provides a proxy to control access or defer work; a strategy pattern selects among interchangeable algorithms at runtime; and a command pattern encapsulates a request as an object to decouple the sender from the receiver.