1、定义

组合模式：将对象组成树形结构以表示“整体-部分”的层次结构

写法

//目录抽象类
public abstract class Dir {

    private String name;

    protected List<Dir> dirs = new ArrayList<>(  );

    public Dir(String name){
        this.name = name;
    }

    public abstract void addDir(Dir dir);

    public abstract void rmDir(Dir dir);

    public abstract void clear();

    public abstract void print();

    public abstract List<Dir> getFiles();

    public  String getName(){
        return name;
    }
}


public class File extends Dir{

    public File(String name) {
        super(name);
    }

    @Override
    public void addDir(Dir dir) {
        throw new UnsupportedOperationException("文件对象不支持该操作！");
    }

    @Override
    public void rmDir(Dir dir) {
        throw new UnsupportedOperationException("文件对象不支持该操作！");
    }

    @Override
    public void clear() {
        throw new UnsupportedOperationException("文件对象不支持该操作！");
    }

    @Override
    public void print() {
        System.out.print(getName());
    }

    @Override
    public List<Dir> getFiles() {
        throw new UnsupportedOperationException("文件对象不支持该操作！");
    }

}

public class Folder extends Dir{

    public Folder(String name) {
        super( name );
    }

    @Override
    public void addDir(Dir dir) {
        dirs.add( dir );
    }

    @Override
    public void rmDir(Dir dir) {
        dirs.remove( dir );
    }

    @Override
    public void clear() {
        dirs.clear();
    }

    @Override
    public void print() {
        System.out.print(getName() + "(");
        Iterator<Dir> iter = dirs.iterator();
        while (iter.hasNext()) {
            Dir dir = iter.next();
            dir.print();
            if(iter.hasNext()){
                System.out.print(", ");
            }
        }
        System.out.print(")");
    }

    @Override
    public List<Dir> getFiles() {
        return dirs;
    }
}

public class TestMain {

    /**
     * 组合模式表示 : 整体-部分的关系
     * @param args 树型结构
     */
    public static void main(String[] args) {

        //构造一个目录对象表示C盘根目录
        Dir diskC = new Folder("C");

        //C盘根目录下有一个文件Log.txt
        diskC.addDir(new File("Log.txt"));

        //C盘根目录下有三个目录Windows、PerfLogs、Program File
        Dir dirWin = new Folder("Windows");

        //Windows目录下有文件explorer.exe
        dirWin.addDir(new File("explorer.exe"));
        diskC.addDir(dirWin);

        //打印出文件结构
        diskC.print();

    }

}

代码示例

https://github.com/yinlingchaoliu/23-design-pattern