实现一个简单的策略模式

ゝ一纸荒年。 2023-06-26 08:27 10阅读 0赞

这里我打算用三种方式来实现，分别是

1.  正常写法
2.  匿名类写法
3.  Lambda写法

先说明一下场景，我想筛选苹果，按照苹果的重量和颜色，可能按照重量，也可能按照颜色，也可能是颜色和重量。

## 正常写法 ##

**Aapple**实体类

@Data
    public class Apple {
        private String color;
        private int weight;
        private Long apId;
    }

接口**ApplePredicate**

public interface ApplePredicate {
        boolean test(Apple apple);
    }

**AppleColorPredicate**（根据苹果颜色筛选，假如为红色）

public class AppleColorPredicate implements ApplePredicate {
        @Override
        public boolean test(Apple apple) {
            return "red".equals(apple.getColor());
        }
    }

**AppleWeightPredicate**（根据苹果重量筛选，假如要大于150）

public class AppleWeightPredicate implements ApplePredicate{
        @Override
        public boolean test(Apple apple) {
            return apple.getWeight()>150;
        }
    }

**FilterApples**测试类

public class FilterApples {
    
        public static List<Apple> filterApples(List<Apple> apples, ApplePredicate ap){
            List<Apple> result = new ArrayList<>();
            for (Apple apple:apples){
                if (ap.test(apple))
                    result.add(apple);
            }
            return result;
        }
    
        public void test(){
            //定义两个苹果放入List
            List<Apple> apples = new ArrayList<>();
            Apple appleOne = new Apple();
            appleOne.setColor("red");
            appleOne.setWeight(200);
            Apple appleTwo = new Apple();
            appleTwo.setColor("blue");
            appleTwo.setWeight(50);
            apples.add(appleOne);
            apples.add(appleTwo);
            //这里选择筛选条件（这里为根据苹果重量）
            List<Apple> applesFilteredOne = filterApples(apples, new AppleWeightPredicate());
            System.out.println(applesFilteredOne);
        }
    
        public static void main(String[] args) {
            FilterApples filterApples = new FilterApples();
            filterApples.test();
        }
    }

打印输出  
![在这里插入图片描述][20191231095028289.png]  
我们可以看到把重量大于150的苹果给筛选出来了。

## 匿名类写法 ##

**Aapple**实体类

@Data
    public class Apple {
        private String color;
        private int weight;
        private Long apId;
    }

接口**ApplePredicate**

public interface ApplePredicate {
        boolean test(Apple apple);
    }

**FilterApples**测试类

public class FilterApples {
    
        public static List<Apple> filterApples(List<Apple> apples, ApplePredicate ap){
            List<Apple> result = new ArrayList<>();
            for (Apple apple:apples){
                if (ap.test(apple))
                    result.add(apple);
            }
            return result;
        }
    
        public void test(){
            //定义两个苹果放入List
            List<Apple> apples = new ArrayList<>();
            Apple appleOne = new Apple();
            appleOne.setColor("red");
            appleOne.setWeight(200);
            Apple appleTwo = new Apple();
            appleTwo.setColor("blue");
            appleTwo.setWeight(50);
            apples.add(appleOne);
            apples.add(appleTwo);
            //这里选择筛选条件（这里为根据苹果颜色且为蓝色）
            List<Apple> applesFilteredTwo = filterApples(apples, new ApplePredicate() {
                //重写test
                @Override
                public boolean test(Apple apple) {
                    return "blue".equals(apple.getColor());
                }
            });
            System.out.println(applesFilteredTwo);
        }
    
        public static void main(String[] args) {
            FilterApples filterApples = new FilterApples();
            filterApples.test();
        }
    }

打印输出  
![在这里插入图片描述][20191231095543721.png]  
我们发现，使用匿名类写法不需要再写接口的实现类了，而是直接进行编写条件，但是他很笨重，占用了很大的空间。

## Lambda写法 ##

**Aapple**实体类

@Data
    public class Apple {
        private String color;
        private int weight;
        private Long apId;
    }

接口**ApplePredicate**

public interface ApplePredicate {
        boolean test(Apple apple);
    }

**FilterApples**测试类

public class FilterApples {
    
        public static List<Apple> filterApples(List<Apple> apples, ApplePredicate ap){
            List<Apple> result = new ArrayList<>();
            for (Apple apple:apples){
                if (ap.test(apple))
                    result.add(apple);
            }
            return result;
        }
    
        public void test(){
            //定义两个苹果放入List
            List<Apple> apples = new ArrayList<>();
            Apple appleOne = new Apple();
            appleOne.setColor("red");
            appleOne.setWeight(200);
            Apple appleTwo = new Apple();
            appleTwo.setColor("blue");
            appleTwo.setWeight(50);
            apples.add(appleOne);
            apples.add(appleTwo);
            //lambda
            List<Apple> applesFilteredThree = filterApples(apples,(Apple apple) -> "red".equals(apple.getColor()));
    
            System.out.println(applesFilteredThree);
        }
    
        public static void main(String[] args) {
            FilterApples filterApples = new FilterApples();
            filterApples.test();
        }
    }

打印输出  
![在这里插入图片描述][20191231100017881.png]  
Lambda更为简单，而且代码可读性更强。

## 总结 ##

我们发现三种的主要不同的地方为这里

//正常写法
            List<Apple> applesFilteredOne = filterApples(apples, new AppleWeightPredicate());
            //匿名类写法
            List<Apple> applesFilteredTwo = filterApples(apples, new ApplePredicate() {
                //重写test
                @Override
                public boolean test(Apple apple) {
                    return "blue".equals(apple.getColor());
                }
            });
            //lambda
            List<Apple> applesFilteredThree = filterApples(apples,(Apple apple) -> "red".equals(apple.getColor()));

正常写法，还需要去看实现类的判别条件。  
匿名类写法，比较笨重。  
lambda，可读性强，代码简单。

lambda具体学习可以去看《java8实战》

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![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JheHhkd3lw_size_16_color_FFFFFF_t_70]

[20191231095028289.png]: https://img-blog.csdnimg.cn/20191231095028289.png
[20191231095543721.png]: https://img-blog.csdnimg.cn/20191231095543721.png
[20191231100017881.png]: https://img-blog.csdnimg.cn/20191231100017881.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JheHhkd3lw_size_16_color_FFFFFF_t_70]: https://img-blog.csdnimg.cn/20200113173907687.jpg?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JheHhkd3lw,size_16,color_FFFFFF,t_70