组合模式：说白了就是统一接口的树状结构。

好处就是树结构的类无论是枝干还是树叶使用统一的接口，当要对这些类进行操作的时候就可以用同一套代码了。

abstract class Componet{
    protected String name;
    
    public Component(String name){
        this.name = name;
    }
    
    public abstract void add(Component c);
    public abstract void remove(Component c);
    public abstract void Display(int depth);
}

class Leaf extends Component{
    
    public Leaf(String name){
        super.Component(name);
    }

    public void add(){
        System.out.println("不能添加叶子");
    }

    public void remove(Component c){
        System.out.println("不能从叶子中移除");
    }

    public void display(int depth){
        
        String s = "-";
        for(int i = 0;i < depth ; i++){
            s = s + "--";
        }
        System.out.println(s);
    }
}

class Composite extend Component{
    private List<Component>children = new List<Component>();

    public Composite(String name){
        super.Composite(name);
    }

    public void add(Component c){
        this.add(c);
    }

    public void remove(Component c){
        this.remove(c);
    }
    
    public void display(int depth){
        String s = "-";
        for(int i = 0;i < depth ; i++){
            s = s + "--";
        }
        System.out.println(s);

        foreach (Component c : children){
            c.display();
        }
    }
}

public class Test{
    public static void main(String[] args){
        Composite root = new Composite("root");
        root.add(new Leaf("Leaf A"));
        root.add(new Leaf("Leaf B"));

        Composite comp = new Composite("Composite X");
        comp.add(new Leaf("Leaf XA"));
        comp.add(new Leaf("Leaf XB"));

        root.add(comp);
        
        Composite comp2 = new Composite("Composite XY");
        comp2.add(new Leaf("Leaf XYA"));
        comp2.add(new Leaf("Leaf XYB"));

        root.add(comp2);

        root.add(new Leaf("Leaf C"));
        Leaf leaf = new Leaf("Leaf D");
        root.add(leaf);
        root.remove(leaf);
        
        root.display();
    }
}