结构型模式 --- 组合模式

将对象组合成树状的层次结构的模式，用来表示“部分-整体”的关系，使用户对单个对象和组合对象具有一致的访问性

package study.org;

import java.util.ArrayList;

public class Demo {
    public static void main(String[] args) {
        Composite component = new Composite();
        
        Leaf leaf1 = new Leaf();
        leaf1.tag = "1";
        component.add(leaf1);
        
        Leaf leaf2 = new Leaf();
        leaf2.tag = "2";
        component.add(leaf2);
        
        Composite component1 = new Composite();
        
        Leaf leaf3 = new Leaf();
        leaf3.tag = "3";
        component1.add(leaf3);
        
        component.add(component1);
        
        component.operation();

    }
}

abstract class Component {
    public abstract void add(Component c); // 增加成员

    public abstract void remove(Component c); // 删除成员

    public abstract Component getChild(int i); // 获取成员

    public abstract void operation(); // 业务方法
}

class Leaf extends Component {
    String tag;
    
    public void add(Component c) {
        // 异常处理或错误提示
    }

    public void remove(Component c) {
        // 异常处理或错误提示
    }

    public Component getChild(int i) {
        // 异常处理或错误提示
        return null;
    }

    public void operation() {
        System.out.println(tag);
    }
}

class Composite extends Component {  
    private ArrayList<Component> list = new ArrayList<Component>();  
      
    public void add(Component c) {  
        list.add(c);  
    }  
      
    public void remove(Component c) {  
        list.remove(c);  
    }  
      
    public Component getChild(int i) {  
        return (Component)list.get(i);  
    }  
      
    public void operation() {  
        //容器构件具体业务方法的实现  
        //递归调用成员构件的业务方法  
        for(Object obj:list) {  
            ((Component)obj).operation();  
        }  
    }     
}