解决的问题

将对象组合成层级结构，支持一起修改。例如文件结构：Root Folder下有两个文件夹：Videos Folder和Images Folder，Videos Folder下存放视频文件，Images Folder下存放图片文件。当删除Root Folder时，会删除他里面的所有文件。

代码

File:

package com.cong.designpattern.composite;

public interface File {
    public void delete();
}

Folder:

package com.cong.designpattern.composite;

import java.util.ArrayList;
import java.util.List;

public class Folder implements File {
    private List<File> files = new ArrayList<>();
    @Override
    public void delete() {
        for (File file : this.files) file.delete();
        System.out.println("Delete folder");
    }
    public void add(File file) {
        this.files.add(file);
    }
}

Image:

package com.cong.designpattern.composite;

public class Image implements File{
    @Override
    public void delete() {
        System.out.println("Delete image");
    }
}

Video:

package com.cong.designpattern.composite;

public class Video implements File{
    @Override
    public void delete() {
        System.out.println("Delete video");
    }
}

Test code:

Folder imagesFolder = new Folder();
Image image = new Image();
imagesFolder.add(image);

Folder videosFolder = new Folder();
Video video = new Video();
videosFolder.add(video);

Folder rootFolder = new Folder();
rootFolder.add(imagesFolder);
rootFolder.add(videosFolder);

rootFolder.delete();

UML

Composite Pattern UML