Composite

The composite pattern is a partitioning design pattern, describing a group of objects that are treated the same way as a single instance of the same type of object . The intent of a composite is to "compose" objects into tree structures to represent part-whole hierarchies. Implementing the composite pattern lets clients treat individual objects and compositions uniformly.

Overview

What problems can the Composite design pattern solve?
• A part-whole hierarchy should be represented so that clients can treat part and whole objects uniformly.
• A part-whole hierarchy should be represented as tree structure.

What solution does the Composite design pattern describe?
1. Define a unified Component interface for both part (Leaf) objects and whole (Composite) objects.
2. Individual Leaf objects implement the Component interface directly, and Composite objects forward requests to their child components.

This enables clients to work through the Component interface to treat Leaf and Composite objects uniformly: Leaf objects perform a request directly, while Composite objects forward the request to their child components recursively downwards the tree structure. This makes client classes easier to implement, change, test and reuse.