开闭原则

• 定义： 一个软件实体如类，模块，和函数应该对扩展开放，对修改关闭。

• 用抽象构建框架，用实现扩展细节

• 优点： 提高软件系统的可复用性及可维护性

开闭原则.png

---

package com.design.principle.openclose;

/***
 * 课程接口
 */
public interface ICourse{

    /** 获取课程ID */
    public Integer getId() ;

    /** 获取课程名称 */
    public String getName() ;

    /** 获取课程价格 */
    public Double getPrice() ;

}

package com.design.principle.openclose;

/***
 * Java 课程
 */
public class JavaCourse implements ICourse {

    /** 课程ID */
    private Integer id;

    /** 课程名称 */
    private String name;

    /** 课程价格 */
    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 id;
    }

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

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

    @Override
    public String toString() {
        return "JavaCourse{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", price=" + price +
                '}';
    }
}

package com.design.principle.openclose;

/***
 *  Flutter 课程
 */
public class FlutterCourse implements ICourse {

    /** 课程ID */
    private Integer id;

    /** 课程名称 */
    private String name;

    /** 课程价格 */
    private Double price;


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


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

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

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

    @Override
    public String toString() {
        return "FlutterCourse{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", price=" + price +
                '}';
    }
}

package com.design.principle.openclose;

/***
 * Java 课程
 */
public class JavaCourseDiscount extends JavaCourse {


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

    /***
     * 折扣后价格
     * @return
     */
    public Double getDiscountPrice() {
        return super.getPrice()*0.8;
    }



}

package com.design.principle.openclose;

public class Test {

    public static void main(String[] args) {

        // 1 获取Java课程的信息

        ICourse course = new JavaCourse(1,"java",12.00);

        System.out.println("Java课程id"+course.getId());
        System.out.println("Java课程name"+course.getName());
        System.out.println("Java课程price"+course.getPrice());

        System.out.println();
        System.out.println();
        System.out.println();

        // 要求只对Java课程的价格打8折

        ICourse courseDiscount = new JavaCourseDiscount(1,"java",12.00);
        JavaCourseDiscount javaCourseDiscount = (JavaCourseDiscount) courseDiscount;
        System.out.println("Java课程id"+javaCourseDiscount.getId());
        System.out.println("Java课程name"+javaCourseDiscount.getName());
        System.out.println("Java课程price"+javaCourseDiscount.getPrice());
        System.out.println("Java课程discountPrice"+javaCourseDiscount.getDiscountPrice());

    }


}