设计模式-组合（Composite）模式

主要角色

• 抽象聚合类
• 复合物

职责

类的层次结构更清晰和明确。

类图

类关系示意图

代码

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

    @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.print("  ");
                }
            }
            catalogComponent.print();
        }
    }
}
---
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);
    }
}

使用

public class Test {
    public static void main(String[] args) {
        CatalogComponent linuxCourse = new Course("Linux课程",11);
        CatalogComponent windowsCourse = new Course("Windows课程",11);

        CatalogComponent javaCourseCatalog = new CourseCatalog("Java课程目录",2);

        CatalogComponent mmallCourse1 = new Course("Java电商一期",55);
        CatalogComponent mmallCourse2 = new Course("Java电商二期",66);
        CatalogComponent designPattern = new Course("Java设计模式",77);

        javaCourseCatalog.add(mmallCourse1);
        javaCourseCatalog.add(mmallCourse2);
        javaCourseCatalog.add(designPattern);

        CatalogComponent imoocMainCourseCatalog = new CourseCatalog("慕课网课程主目录",1);
        imoocMainCourseCatalog.add(linuxCourse);
        imoocMainCourseCatalog.add(windowsCourse);
        imoocMainCourseCatalog.add(javaCourseCatalog);

        imoocMainCourseCatalog.print();
    }
}

技巧

• 一个类即继承也有这个类的实例，很有可能是组合模式