定义：将对象组合成树形结构以表示  部分--整体的层次结构

组合模式使客户端对单个对象和组合对象保持一致的方式处理

类型：结构型

优点：

1.清楚地定义分层次的复杂对象，表示对象的全部去或部分层次

2.让客户端忽略了层次的差异，方便对整个层次结构进行控制

3.简化客户端代码

4.符合开闭原则

public abstract class CatalogComponent {
    public void add(CatalogComponent catalogComponent){
        throw new UnsupportedOperationException("不支持添加操作");
    }
    public void remove(CatalogComponent catalogComponent){
        throw new UnsupportedOperationException("不支持删除操作");
    }
    public String getName(CatalogComponent catalogComponent){
        throw new UnsupportedOperationException("不支持获取名称操作");
    }
    public double getPrice(CatalogComponent catalogComponent){
        throw new UnsupportedOperationException("不支持获取价格操作");
    }
    public void print(){
        throw  new UnsupportedOperationException("不支持打印操作");
    }
}

public class Course extends CatalogComponent {
    private  String name;
    private  double price;

    public Course(String name, double price) {
        this.name = name;
        this.price = price;
    }

    @Override
    public String getName(CatalogComponent catalogComponent) {
        return this.name;
    }

    @Override
    public double getPrice(CatalogComponent catalogComponent) {
        return this.price;

    }

    @Override
    public void print() {
        System.out.println("Course Name:"+name+" price:"+price);
    }
}

public class CourseCatalog extends  CatalogComponent{
    private List<CatalogComponent> items=new ArrayList<CatalogComponent>();
    private  String name;
    private  Integer level;

    public CourseCatalog(String name,Integer level) {
        this.name = name;
        this.level=level;
    }

    @Override
    public void add(CatalogComponent catalogComponent) {
        items.add(catalogComponent);
    }

    @Override
    public void remove(CatalogComponent catalogComponent) {
        items.remove(catalogComponent);
    }

    @Override
    public void print() {
        System.out.println(this.name);
        for(CatalogComponent catalogComponent:items){
            if(this.level!=null){
                for(int i=0;i<this.level;i++){
                    System.out.println("   ");
                }
            }
            catalogComponent.print();
        }
    }
}