Composite Pattern - Example

Example

The following example, written in Java, implements a graphic class, which can be either an ellipse or a composition of several graphics. Every graphic can be printed. In algebraic form,

Graphic = ellipse | GraphicList GraphicList = empty | Graphic GraphicList

It could be extended to implement several other shapes (rectangle, etc.) and methods (translate, etc.).

/** "Component" */ interface Graphic { //Prints the graphic. public void print; } /** "Composite" */ import java.util.List; import java.util.ArrayList; class CompositeGraphic implements Graphic { //Collection of child graphics. private List childGraphics = new ArrayList; //Prints the graphic. public void print { for (Graphic graphic : childGraphics) { graphic.print; } } //Adds the graphic to the composition. public void add(Graphic graphic) { childGraphics.add(graphic); } //Removes the graphic from the composition. public void remove(Graphic graphic) { childGraphics.remove(graphic); } } /** "Leaf" */ class Ellipse implements Graphic { //Prints the graphic. public void print { System.out.println("Ellipse"); } } /** Client */ public class Program { public static void main(String args) { //Initialize four ellipses Ellipse ellipse1 = new Ellipse; Ellipse ellipse2 = new Ellipse; Ellipse ellipse3 = new Ellipse; Ellipse ellipse4 = new Ellipse; //Initialize three composite graphics CompositeGraphic graphic = new CompositeGraphic; CompositeGraphic graphic1 = new CompositeGraphic; CompositeGraphic graphic2 = new CompositeGraphic; //Composes the graphics graphic1.add(ellipse1); graphic1.add(ellipse2); graphic1.add(ellipse3); graphic2.add(ellipse4); graphic.add(graphic1); graphic.add(graphic2); //Prints the complete graphic (four times the string "Ellipse"). graphic.print; } }

The following example, written in C#.

namespace CompositePattern { using System; using System.Collections.Generic; using System.Linq; //Client class Program { static void Main(string args) { // initialize variables var compositeGraphic = new CompositeGraphic; var compositeGraphic1 = new CompositeGraphic; var compositeGraphic2 = new CompositeGraphic; //Add 1 Graphic to compositeGraphic1 compositeGraphic1.Add(new Ellipse); //Add 2 Graphic to compositeGraphic2 compositeGraphic2.AddRange(new Ellipse, new Ellipse); /*Add 1 Graphic, compositeGraphic1, and compositeGraphic2 to compositeGraphic */ compositeGraphic.AddRange(new Ellipse, compositeGraphic1, compositeGraphic2); /*Prints the complete graphic (four times the string "Ellipse").*/ compositeGraphic.Print; Console.ReadLine; } } //Component public interface IGraphic { void Print; } //Leaf public class Ellipse : IGraphic { //Prints the graphic public void Print { Console.WriteLine("Ellipse"); } } //Composite public class CompositeGraphic : IGraphic { //Collection of Graphics. private readonly List _Graphics; //Constructor public CompositeGraphic { //initialize generic Colleciton(Composition) _Graphics = new List; } //Adds the graphic to the composition public void Add(IGraphic graphic) { _Graphics.Add(graphic); } //Adds multiple graphics to the composition public void AddRange(params IGraphic graphic) { _Graphics.AddRange(graphic); } //Removes the graphic from the composition public void Delete(IGraphic graphic) { _Graphics.Remove(graphic); } //Prints the graphic. public void Print { foreach (var childGraphic in _Graphics) { childGraphic.Print; } } } }

Read more about this topic:  Composite Pattern

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