Compose objects into tree structures to represent part-whole hierarchies. Composite lets clients treat individual objects and compositions of objects uniformly.
将对象组合成树形结构以表示“部分-整体”的层次结构，使得用户对单个对象和组合对象的使用具有一致性。
The classes and objects participating in this pattern are:
- declares the interface for objects in the composition.
- implements default behavior for the interface common to all classes, as appropriate.
- declares an interface for accessing and managing its child components.
- (optional) defines an interface for accessing a component's parent in the recursive structure, and implements it if that's appropriate.
- represents leaf objects in the composition. A leaf has no children.
- defines behavior for primitive objects in the composition.
- defines behavior for components having children.
- stores child components.
- implements child-related operations in the Component interface.
- manipulates objects in the composition through the Component interface.