> Design Patterns > Composite Design Pattern

Composite Design Pattern

Composite design pattern is used to handle primitive and composite objects uniformly.

Intent

Compose objects into tree structures to represent part-whole hierarchies. Composite lets clients treat individual objects and compositions of objects uniformly.

The intent is to compose the object to present part-whole hierarchy and handle both primitive and composite object uniformly.

Problem

The primitive and composite objects have to be handled differently. To distinguish these objects for manipulation increases the complexity.

Solution

Come up with a way to manipulate the primitive and composite object uniformly.

That means both the primitive and composite object have to be handled in similar manner.

Where it is applicable?

When part-whole hierarchy of object has to be represented.
Wherever primitive and composite objects have to be handled in similar manner.
Directories and Files in File system are the best example.

Structure

This is the UML structure of Composite design pattern-

Participant classes

Component class provides the interface Operation().
Concrete classes Leaf and Composite implements the method Operation().

How they work together?

Composite has instance of the class Component. It has objects which can be Leaf and Composite as well. It traverses them and does the operation on all the elements it has composed, either primitive or composite.
The method Add(), Remove() and GetChild() can be provided in Component or Composite, its transparency vs safety. Providing it in Component class makes it transparent and providing it in Composite class makes it safe.
So you can see both the primitive and composite objects are handled in similar manner.

Example

Implementation Code

C++	Composite Pattern in C++	Composite Pattern C++ Example
C#	Composite Pattern in C#	Composite Pattern C# Example
Java	Composite Pattern in Java	Composite Pattern Java Example
Python	Composite Pattern in Python	Composite Pattern Python Example
JavaScript	Composite Pattern in JavaScript	Composite Pattern JavaScript Example
PHP	Composite Pattern in PHP	Composite Pattern PHP Example
Ruby	Composite Pattern in Ruby	Composite Pattern Ruby Example
Swift	Composite Pattern in Swift	Composite Pattern Swift Example
Objective-C	Composite Pattern in Objective-C	Composite Pattern Objective-C Example

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Suresh Kumar Srivastava is founder of online learning site coursegalaxy.com and author of popular books "C In Depth", "Data Structures Through C In Depth". He has 18+ years experience in industry and worked on architecture and design of multiple products. This article is from his courses on Design Patterns.