Composite Pattern

Overview

Participants

Component

• 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.
• this participant can not be an interface.

Leaf

• represents leaf objects in the composition. A leaf has no children.
• defines behavior for primitive objects in the composition.
• this participant can not be read-only.
• this participant can not be an interface.

Composite

• defines behavior for components having children.
• stores child component.
• implements child-related operations in the component interface.
• this participant can not be read-only.
• this participant can not be an interface.

Parameters

Components Container

• here you can specify the name of the Composite's Vector attribute, used to keep references to the Component objects, contained within the Composite.

Children Enumeration Method

• here you can specify the name of the Composite's method for returning an enumeration of Component objects, contained within the Composite.

Create Pattern Links

• when selected, will create special JavaDoc links in the code between pattern participants, describing their relationships.

Applicability

• you want to represent part-whole hierarchies of objects.
• you want clients to be able to ignore the difference between compositions of objects and individual objects. Clients will treat all objects in the composite structure uniformly.