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Design pattern in software engineering
In software engineering, the composite pattern is a partitioning design pattern. The composite pattern describes a group of objects that are treated the same way as a single instance of the same type of object. The intent of a composite is to "compose" objects into tree structures to represent part whole hierarchies. Implementing the composite pattern lets clients treat individual objects and compositions uniformly.

A part whole hierarchy should be represented so that clients can treat part and whole objects uniformly. A part whole hierarchy should be represented as tree structure. When defining (1) Part objects and (2) Whole objects that act as containers for Part objects, clients must treat them separately, which complicates client code.

When dealing with Tree structured data, programmers often have to discriminate between a leaf node and a branch. This makes code more complex, and therefore, more error prone. The solution is an interface that allows treating complex and primitive objects uniformly. In object oriented programming, a composite is an object designed as a composition of one or more similar objects, all exhibiting similar functionality. This is known as a "has a" relationship between objects. The key concept is that you can manipulate a single instance of the object just as you would manipulate a group of them. The operations you can perform on all the composite objects often have a least common denominator relationship. For example, if defining a system to portray grouped shapes on a screen, it would be useful to define resizing a group of shapes to have the same effect (in some sense) as resizing a single shape.

As it is described in Design Patterns, the pattern also involves including the child manipulation methods in the main Component interface, not just the Composite subclass. More recent descriptions sometimes omit these methods.