设计模式六大原则之开闭原则

1.基本介绍

• 一个软件实体如类，模块和函数应该对扩展开放（对于提供方来说），对修改关闭（对于使用方来说）。用抽象

  构建框架，用实现扩展细节。

• 当软件需要变化时，尽量通过扩展软件实体的行为来实现变化，而不是通过修改已有的代码来实现变化

2.基本代码实现

public class Ocp {
    public static void main(String[] args) {
        GraphicEditor graphicEditor = new GraphicEditor();
        graphicEditor.drawShape(new Rectangle());
        graphicEditor.drawShape(new Circle());
    }

   public static class GraphicEditor{
        public void drawShape(Shape s){
            if (s.m_type ==1) drawRectangle(s);
            else if (s.m_type ==2) drawCircle(s);
        }

        private void drawCircle(Shape s) {
            System.out.println("绘制圆形");
        }

        private void drawRectangle(Shape s) {
            System.out.println("绘制矩形");
        }
    }
    //Shape类，基类
  public static class Shape {int m_type;}
   public static class Rectangle extends Shape{
        Rectangle(){
            super.m_type =1;
        }
    }
    public  static class Circle extends Shape{
        Circle(){
            super.m_type =2;
        }
    }
}

3.在基础代码基础上新增功能，话三角形

public class Ocp { 【使用方】
    public static void main(String[] args) {
        GraphicEditor graphicEditor = new GraphicEditor();
        graphicEditor.drawShape(new Rectangle());
        graphicEditor.drawShape(new Circle());
        //新增的代码
        graphicEditor.drawShape(new Triangle());
    }

   public static class GraphicEditor{
        public void drawShape(Shape s){
            if (s.m_type ==1) drawRectangle(s);
            else if (s.m_type ==2) drawCircle(s);
            //新增的代码
            else if (s.m_type ==3) drawTriangle(s);
        }

        private void drawCircle(Shape s) {
            System.out.println("绘制圆形");
        }

        private void drawRectangle(Shape s) {
            System.out.println("绘制矩形");
        }
        //新增的代码
       private void drawTriangle(Shape s) {
           System.out.println("绘制三角形");
       }
    }
    //Shape类，基类
  public static class Shape {int m_type;}
   public static class Rectangle extends Shape{
        Rectangle(){
            super.m_type =1;
        }
    }
    public  static class Circle extends Shape{
        Circle(){
            super.m_type =2;
        }
    }
    //新增的代码
    public  static class Triangle extends Shape{
        Triangle(){
            super.m_type=3;
        }
    }
}

可发现，当新增一个图形时，需要修改的地方太多，不符合开闭原则

4.基于OCP原则改进

package com.example.springboottest.openclose;

public class improve {
    public static void main(String[] args) {
        graphicEditor graphicEditor = new graphicEditor();
        graphicEditor.drawShape(new Rectangle());
        graphicEditor.drawShape(new Circle());
        graphicEditor.drawShape(new Triangle());
    }
    public static class graphicEditor{
        public void drawShape(Shape s) {
            s.draw();
        }
    }

    public static  abstract class Shape{
        int m_type;
        public abstract void draw();
    }
    public static class Rectangle extends Shape{
        public Rectangle() {
            super.m_type =1;
        }
        @Override
        public void draw() {
            System.out.println("绘制矩形");
        }
    }
    public static class Circle extends Shape{
        public Circle() {
            super.m_type =2;
        }
        @Override
        public void draw() {
            System.out.println("绘制圆形");
        }
    }
    public static class Triangle extends Shape{
        public Triangle() {
            super.m_type =3;
        }
        @Override
        public void draw() {
            System.out.println("绘制三角形");
        }
    }

}

我们可以发现，当我们新增一个图形时，只需要重新写一个接口去实现，而不需要在修改源代码的基础上进行

功能的拓展。

参考：https://www.cnblogs.com/rmxd/p/12541911.html