场景

我们需要画一个图形，可选的策略就是用红色笔来画，还是绿色笔来画，亦或者蓝色笔来画

实现

项目结构：
image.png
首先，先定义一个策略接口：

  1. public interface Strategy {
  2.     public int draw(int radius, int x, int y);
  3. }

然后我们定义具体的几个策略：

  1. public class RedPen implements Strategy {
  2.     @Override
  3.     public int draw(int radius, int x, int y) {
  4.         System.out.println("用红色色笔画图，radius:" + radius + ", x:" + x + ", y:" + y);
  5.         return radius;
  6.     }
  7. }
  9. public class GreenPen implements Strategy {
  10.     @Override
  11.     public int draw(int radius, int x, int y) {
  12.         System.out.println("用绿色笔画图，radius:" + radius + ", x:" + x + ", y:" + y);
  13.         return radius;
  14.     }
  15. }
  17. public class BluePen implements Strategy {
  18.     @Override
  19.     public int draw(int radius, int x, int y) {
  20.         System.out.println("用蓝色笔画图，radius:" + radius + ", x:" + x + ", y:" + y);
  21.         return radius;
  22.     }
  23. }

使用策略的类：

  1. public class Context {
  2.     private Strategy strategy;
  4.     public Context(Strategy strategy){
  5.         this.strategy = strategy;
  6.     }
  8.     public int executeDraw(int radius, int x, int y){
  9.         return strategy.draw(radius, x, y);
  10.     }
  12.     public static void main(String[] args) {
  13.         // 使用蓝色笔来画
  14.         Context context = new Context(new BluePen());
  15.         // 输出：用蓝色笔画图，radius:10, x:0, y:0
  16.         context.executeDraw(10, 0, 0);
  17.     }
  18. }