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<TreeNode> children = new Vector<TreeNode>();
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<TreeNode> 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 ===
<source lang=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<Graphic> childGraphics = new ArrayList<Graphic>();

//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();
}
}

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