23种设计模式 第二部分 结构模式（6）组合模式

理解

组合模式有时又叫部分-整体模式在处理类似树形结构的问题时比较方便。

实现

import java.util.Enumeration;
import java.util.Vector;

public class TreeNode {
	private String name;
	private TreeNode parent;
	private Vector children = new Vector();
	public TreeNode(String name){
		this.name = name;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public TreeNode getParent() {
		return parent;
	}
	public void setParent(TreeNode parent) {
		this.parent = parent;
	}
	public void add(TreeNode node){
		children.add(node);
	}
	public void remove(TreeNode node){
		children.remove(node);
	}
	public Enumeration getChildren(){
		return children.elements();
	}
}

public class Tree {
	TreeNode root = null;
	public Tree(String name){
		root = new TreeNode(name);
	}
	public static void main(String[] args){
		Tree tree = new Tree("A");
		TreeNode nodeB = new TreeNode("B");
		TreeNode nodeC = new TreeNode("C");
		
		nodeB.add(nodeC);
		tree.root.add(nodeB);
		System.out.println("build the tree");
	}
}

使用场景：将多个对象组合在一起进行操作，常用于表示树形结构中，例如二叉树，数等。

维基百科

The composite pattern is a partitioning design pattern. The composite pattern describes that a group of objects is to be treated in the same wayas a single instance of an object.

=== Java ===

/** "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();
    }
}