Composition In Java

Composition:

• Method of reuse in which new functionality is obtained by
  creating an object composed of other objects
• The new functionality is obtained by delegating functionality to
  one of the objects being composed
• Sometimes called aggregation or containment, although some
  authors give special meanings to these terms
• For example:

                Aggregation - when one object owns or is responsible for another object
                  and both objects have identical lifetimes (GoF)
               Aggregation - when one object has a collection of objects that can exist on
                their own (UML)
               Containment - a special kind of composition in which the contained object
               is hidden from other objects and access to the contained object is only via
               the container object (Coad)