示例类图

组合模式.png

示例代码

整个树形结构中节点的抽象

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");
    }

}

叶子节点的抽象

• 所谓单个对象；

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);
    }

}

非叶子节点的抽象

• 所谓组合对象；

import java.util.ArrayList;
import java.util.List;

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();
        }
    }

}

客户端面向节点抽象的编程

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();
    }
}

输出：

慕课网课程主目录
Course Name:Linux课程 Price:11.0
Course Name:Windows课程 Price:11.0
Java课程目录
Course Name:Java电商一期 Price:55.0
Course Name:Java电商二期 Price:66.0
Course Name:Java设计模式 Price:77.0