Java8 in Action chap2

通过行为参数化传递代码

1.行为参数化定义：

可以帮助你处理频繁变更的需求的一种软件开发模式。
一个方法可以接收不同行为作为参数，然后去执行。

2.学习这个能做什么？

对你的现有代码进行改进：
从而更灵活适应不断变化的需求。

package lambdasinaction.chap2;

import java.util.*;

/**
 * @author jincheng
 * @date 2019/12/30
 * java in action chap2
 * 思路：通过行为参数化传递代码 + 简单的策略模式
 */
public class FilteringApples{

    public static void main(String ... args){

        List<Apple> inventory = Arrays.asList(new Apple(80,"green"), new Apple(155, "green"), new Apple(120, "red"));   

        // [Apple{color='green', weight=80}, Apple{color='green', weight=155}]
        List<Apple> greenApples = filterApplesByColor(inventory, "green");
        System.out.println(greenApples);

        // [Apple{color='red', weight=120}]
        List<Apple> redApples = filterApplesByColor(inventory, "red");
        System.out.println(redApples);

        // [Apple{color='green', weight=80}, Apple{color='green', weight=155}]
        List<Apple> greenApples2 = filter(inventory, new AppleColorPredicate());
        System.out.println(greenApples2);

        // [Apple{color='green', weight=155}]
        List<Apple> heavyApples = filter(inventory, new AppleWeightPredicate());
        System.out.println(heavyApples);

        // []
        List<Apple> redAndHeavyApples = filter(inventory, new AppleRedAndHeavyPredicate());
        System.out.println(redAndHeavyApples);

        // [Apple{color='red', weight=120}]
        List<Apple> redApples2 = filter(inventory, new ApplePredicate() {
            public boolean test(Apple a){
                return a.getColor().equals("red"); 
            }
        });
        System.out.println(redApples2);

    }

    public static List<Apple> filterGreenApples(List<Apple> inventory){
        List<Apple> result = new ArrayList<>();
        for(Apple apple: inventory){
            if("green".equals(apple.getColor())){
                result.add(apple);
            }
        }
        return result;
    }

    public static List<Apple> filterApplesByColor(List<Apple> inventory, String color){
        List<Apple> result = new ArrayList<>();
        for(Apple apple: inventory){
            if(apple.getColor().equals(color)){
                result.add(apple);
            }
        }
        return result;
    }

    public static List<Apple> filterApplesByWeight(List<Apple> inventory, int weight){
        List<Apple> result = new ArrayList<>();
        for(Apple apple: inventory){
            if(apple.getWeight() > weight){
                result.add(apple);
            }
        }
        return result;
    }


    public static List<Apple> filter(List<Apple> inventory, ApplePredicate p){
        List<Apple> result = new ArrayList<>();
        for(Apple apple : inventory){
            if(p.test(apple)){
                result.add(apple);
            }
        }
        return result;
    }       

    public static class Apple {
        private int weight = 0;
        private String color = "";

        public Apple(int weight, String color){
            this.weight = weight;
            this.color = color;
        }

        public Integer getWeight() {
            return weight;
        }

        public void setWeight(Integer weight) {
            this.weight = weight;
        }

        public String getColor() {
            return color;
        }

        public void setColor(String color) {
            this.color = color;
        }

        public String toString() {
            return "Apple{" +
                    "color='" + color + '\'' +
                    ", weight=" + weight +
                    '}';
        }
    }

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

    static class AppleWeightPredicate implements ApplePredicate{
        public boolean test(Apple apple){
            return apple.getWeight() > 150; 
        }
    }
    static class AppleColorPredicate implements ApplePredicate{
        public boolean test(Apple apple){
            return "green".equals(apple.getColor());
        }
    }

    static class AppleRedAndHeavyPredicate implements ApplePredicate{
        public boolean test(Apple apple){
            return "red".equals(apple.getColor()) 
                    && apple.getWeight() > 150; 
        }
    }
}