Structural Design Pattern: Composite Design Pattern

Define Composite Design Pattern

The Composite pattern is used when we need to treat both a group of items and a single object in the same manner. The composite pattern arranges elements in a tree structure to show both partial and complete hierarchies.

Example of Composite Design Pattern

Examples of composite patterns are:

• File System Folders
• Managers and Employees
• Assemblies

Composite Design pattern with UML diagram

The UML class diagram above includes the following classes, interfaces, and objects:

• Component: This is an abstract class whose members will be implemented by all objects in the hierarchy. It serves as the root class for every object in the hierarchy.
• Composite: This class offers methods for adding, removing, finding, and getting child components.
• Leaf: This class is used to define leaf components within the tree structure, hence they cannot have children.

When to use Composite Design Patterns?

• The composite design pattern is useful for creating hierarchical representations of objects.
• A single item and a collection of objects should be handled the same.
• The Composite pattern is used when data is organized in a tree structure (similar to computer directories).