java 组合模式

[eyes_on_you]

谁可以帮我解释一下这个组合模式啊　还有就是组合模式的具体应用场合啊
希望用比较形象的说法　小弟真的不懂啊

谢谢啦　

package edu.scit.composite;

import java.util.*;

public interface IFile {
public void printName();

public boolean addChild(IFile file);

public boolean removeChild(IFile file);

public List<IFile> getChildren();
}

//树形结构的叶子结点
class File implements IFile{
private String name;

public File(String name) {
this.name = name;
}
public void printName() {
System.out.println(name);
}

public boolean addChild(IFile file) {
return false;
}

public boolean removeChild(IFile file) {
return false;
}

public List<IFile> getChildren() {
return null;
}

}

//树形结构的枝节点
class Folder implements IFile {
private String name;
private List <IFile> childList;

public Folder(String name) {
this.name = name;
this.childList = new ArrayList<IFile>();
}
public void printName() {
System.out.println(name);
}

public boolean addChild(IFile file) {
return childList.add(file);
}

public boolean removeChild(IFile file) {
return childList.remove(file);
}

public List<IFile> getChildren() {
return childList;
}
}


class Client {
public static void main(String[] args) {

//构造一个树形的文件/目录结构
Folder rootFolder = new Folder("c:\\");
Folder compositeFolder = new Folder("composite");
rootFolder.addChild(compositeFolder);
Folder windowsFolder = new Folder("windows");
rootFolder.addChild(windowsFolder);
File file = new File("TestComposite.java");
compositeFolder.addChild(file);

//从rootFolder访问整个对象群
printTree(rootFolder);
}

private static void printTree(IFile ifile) {
ifile.printName();
List <IFile> children = ifile.getChildren();

for (IFile file:children) {
if (file instanceof File) {
System.out.print(" ");
file.printName();
} else if (file instanceof Folder) {
printTree(file);
}
}
}

}

[prince2270]

使用组合模式的一个场合就是：类中使用不同的代码处理单一对象与多个对象。组合模式能够产生可以处理单一对象有可以处理多个对象的代码。简单的说，一组对象与一个对象的处理方法相同。举一个例子：

interface Shape{ void draw();}
class Circle implements Shape{
    public void draw(){ System.out.println("cicle");}
}
class Retangle implements Shape{
    public void draw(){ System.out.println("retangle");}
}
class MoreShape implements Shape{
    private List<Shape> shapes;
    public MoreShape(List<Shape> shapes){this.shapes = shapes;}
    public void draw(){ 
         for(Shape s : shapes)
              s.draw();
    }
}

在这里，对于Circle、Retangle和MoreShape的使用方法，无论是单一对象，还是多个对象，使用方法都是相同的。就是调用它的draw()方法。因为MoreShape也是Shape。