Composite pattern composes objects into tree structures to represent part-whole hierarchies, thus letting clients uniformly treat individual objects and composition objects.
Use composite pattern when the core model of your app can be represented as a tree.
Component interface describes operations that are common to both simple/complex elements of the tree.
- Leaf is a basic element of a tree that doesn't have sub-elements
- does most of the real work since it doesn't have anyone to delegate the work
- Composite element has sub-elements: leaves/composites
- it doesn't know concrete classes of its children, only working with all sub-elements via the
Componentinterface - upon receiving a request, it delegates the work to its sub-elements, process intermediate results, return the final result to client
Client works with all elements through the Component interface.