学习笔记(01):第1章 软件架构设计原则-1.Open-Closed Principle 开闭原则

立即学习:https://edu.youkuaiyun.com/course/play/28942/403588?utm_source=blogtoedu

开闭原则

对扩展开放，修改关闭

eg：接口中定义三个方法分别获取课程的三个属性

public interface ICourse {
    Integer getId();
    String getName();
    Double getPrice();
}

Java课程业务类实现自己的业务

public class JavaCourse implements ICourse {
    private Integer id;
    private String name;
    private Double price;

    public JavaCourse(Integer id, String name, Double price) {
        this.id = id;
        this.name = name;
        this.price = price;
    }

    @Override
    public Integer getId() {
        return this.id;
    }

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

    @Override
    public Double getPrice() {
        return this.price;
    }
}

需求变更：java课程需要打折，根据开闭原则不更改原有代码，创建java打折业务类

public class JavaDiscountCourse extends JavaCourse {

    public JavaDiscountCourse(Integer id, String name, Double price){
        super(id, name, price);
    }

    public Double getDiscountPrice(){
        return super.getPrice() * 0.8;
    }
}

Tips:

这使iCourse获取不到getDiscountPrice方法

ICourse iCourse = new JavaDiscountCourse(1,"Java虚拟机",1180D);

需要

iCourse = (JavaDiscountCourse)iCourse