GOF Intent: To combine objects into a tree structure to represent a hierarchy of "parts of the whole". (form a tree structure)
Role:
1. Component is a unified interface that, where appropriate, implements common default behavior. Declare an interface for accessing multiple leaves.
2.Leaf is the combined object.
3.Composite is a combiner, has a list list, used to store leaf components, and implements operations related to subcomponents in the Component interface, such as adding (add) and deleting (remove).
Implementation: composite is the combiner or combiner (tree-like node), leaf is the combiner (tree-like node). Both implement the same interface.
applicability:
Composite mode applies when:
1. You want to represent the part-whole hierarchy of objects
2. You want users to ignore the difference between composite objects and individual objects, and users will use the same interface uniformly.