一、概念

组合模式也叫合成模式，有时又叫部分-整体模式。只要是树形结构，就要考虑使用组合模式。

二、实例

public abstract class File {
    private String name;
    public File(String name){
        this.name = name;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public abstract void watch();

    /**
     * 组合方法
     *
     */
    public void add(File file){
        throw new UnsupportedOperationException();
    }
    public void del(File file){
        throw new UnsupportedOperationException();
    }
    public File getChild(int position){
        throw new UnsupportedOperationException();
    }
}

public class Folder extends File {
    private List<File> fileList;

    public Folder(String name){
        super(name);
        fileList = new ArrayList<>();
    }

    @Override
    public void watch() {
        StringBuffer sb = new StringBuffer();
        for (File file:fileList){
            sb.append(file.getName() + ";");
        }
        System.out.println("组合模式：这是一个叫" + getName() + "文件夹，包含" + fileList.size() + "个文件，分别是" + sb);
    }

    @Override
    public void add(File file){
        fileList.add(file);
    }
    @Override
    public void del(File file){
        fileList.remove(file);
    }
    @Override
    public File getChild(int position) {
        return fileList.get(position);
    }
}

public class TextFile extends File {
    public TextFile(String name) {
        super(name);
    }

    @Override
    public void watch() {
        System.out.println("组合模式:这是一个叫" + getName() + "文本文件");
    }
}

public class Client {
    public static void main(String[] args) {
        File fileA = new TextFile("a.txt");
        File fileB = new TextFile("b.txt");
        Folder aking = new Folder("king");
        Folder bking = new Folder("kang");
        aking.add(fileA);
        aking.add(fileB);
        bking.add(aking);
        aking.watch();
        bking.watch();
    }
}