Chapter 17. The Composite Pattern

Frequently programmers develop systems in which a component may be either an individual object or a collection of objects. The Composite pattern is designed to accommodate both cases. You can use the Composite to build part-whole hierarchies or to construct data representations of trees. In summary, a composite is a collection of objects, any one of which may be either a composite or just a primitive object. In tree nomenclature, some objects may be nodes with additional branches and some may be leaves.

The problem that develops is the dichotomy between having a single, simple interface to access all the objects in a composite and the ability to distinguish between nodes and leaves. Nodes have children and can ...

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