<< Chapter < Page
  Design patterns   Page 1 / 1
Chapter >> Page >
The Composite Design Pattern is an object-oriented representation of a recursive data structure.


The Composite Design Pattern allows a client object to treat both single components and collections of components identically.    It accomplishes this by creating an abstraction that unifies both the single components and composed collections as abstract equivalents. Mathematically, we say that the single components and composed collections are homomorphically equivalent (from the Latin: homo – same and morph – form ==>to have the same form).

This equivalence of single and composite components is what we call a recursive data structure . In recursive data structures, objects are linked to other objects to create a total object structure made of many “nodes” (objects). Since every node is abstractly equivalent, the entire, possibly infinitely large and complex data structure can be succinctly described in terms of just three distinct things: the single components, the composite components and their abstract representation. This massive reduction in complexity is one of the cornerstones of computer science.

The Composite Design Pattern is an object-oriented representation of a recursive data structure.

Uml diagram and example

In the UML class diagram below, the Client uses an abstract component, AComponent , for some abstract task, operation() .   At run-time, the Client may hold a reference to a concrete component such as Leaf1 or Leaf2 .   When the operation task is requested by the Client , the specific concrete behavior with the particular concrete component referenced will be performed.    

Uml diagram of composite design pattern example

An example of a composite design pattern implementation with 2 single, concrete components and one composite, collection component.

The Composite class is a concrete component like Leaf1 and Leaf2 , but has no operation() behavior of its own.    Instead, Composite is composed with a collection of other abstract components, which may be of any other concrete component type including the composite itself.   The unifying fact is that they are all abstractly AComponent s.   When the operation() method of a Composite object is called, it simply dispatches the request sequentially to all of its "children" components and perhaps, also does some additional computations itself.     For instance, a Composite object could hold references to both a Leaf1 and a Leaf2  instance.   If a client holds a reference to that  Composite object and calls its operation() method, the Composite object will first call operation on its Leaf1 instance and then operation() on its Leaf2 instance.   Thus composite behavior of  Leaf1 plus Leaf2 behaviors is achieved without either duplicating code or by having the Client object knowing that the two leaf components were involved.  

Composite patterns are often used to represent recursive data structures.    The recursive nature of the Composite structure naturally gives way to recursive code to process that structure.

The collection of AComponent s held by Composite , "children", is shown above as an array.   However, the behavior of a Composite pattern is independent of exactly how the collection of AComponents is implemented.   If access speed is not an issue, a vector or a list may be a better implementation choice.    The addChild() and removeChild() methods are optional.

In Design Patterns , the abstract component AComponent is shown as having accessor methods for child AComponent s.   They are not shown here because it is debatable as to whether one wants the Client to fundamentally view the AComponent as a single component or as a collection of components.   Design Patterns models all AComponent s as collections while the above design models them all as single components.   The exact nature of those accessor methods is also debatable.

Questions & Answers

can someone help me with some logarithmic and exponential equations.
Jeffrey Reply
sure. what is your question?
okay, so you have 6 raised to the power of 2. what is that part of your answer
I don't understand what the A with approx sign and the boxed x mean
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
I'm not sure why it wrote it the other way
I got X =-6
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
oops. ignore that.
so you not have an equal sign anywhere in the original equation?
Commplementary angles
Idrissa Reply
im all ears I need to learn
right! what he said ⤴⤴⤴
what is a good calculator for all algebra; would a Casio fx 260 work with all algebra equations? please name the cheapest, thanks.
Kevin Reply
a perfect square v²+2v+_
Dearan Reply
kkk nice
Abdirahman Reply
algebra 2 Inequalities:If equation 2 = 0 it is an open set?
Kim Reply
or infinite solutions?
The answer is neither. The function, 2 = 0 cannot exist. Hence, the function is undefined.
Embra Reply
if |A| not equal to 0 and order of A is n prove that adj (adj A = |A|
Nancy Reply
rolling four fair dice and getting an even number an all four dice
ramon Reply
Kristine 2*2*2=8
Bridget Reply
Differences Between Laspeyres and Paasche Indices
Emedobi Reply
No. 7x -4y is simplified from 4x + (3y + 3x) -7y
Mary Reply
is it 3×y ?
Joan Reply
J, combine like terms 7x-4y
Bridget Reply
im not good at math so would this help me
Rachael Reply
I'm not good at math so would you help me
what is the problem that i will help you to self with?
how do you translate this in Algebraic Expressions
linda Reply
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
Crystal Reply
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
Chris Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
many many of nanotubes
what is the k.e before it land
what is the function of carbon nanotubes?
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
what is system testing
what is the application of nanotechnology?
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
anybody can imagine what will be happen after 100 years from now in nano tech world
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
silver nanoparticles could handle the job?
not now but maybe in future only AgNP maybe any other nanomaterials
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
bamidele Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
Got questions? Join the online conversation and get instant answers!
QuizOver.com Reply

Get the best Algebra and trigonometry course in your pocket!

Source:  OpenStax, Design patterns. OpenStax CNX. Jun 04, 2009 Download for free at http://cnx.org/content/col10678/1.2
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Design patterns' conversation and receive update notifications?