1.2.2 传递代码：一个例子

最新推荐文章于 2025-01-19 18:56:24 发布

原创最新推荐文章于 2025-01-19 18:56:24 发布 · 118 阅读

本文展示了一个使用Java 8的方法引用(FilteringApples::isHeavyApple)来筛选苹果列表的例子，具体实现了根据颜色和重量筛选苹果的功能。通过定义谓词Predicate<Apple>并结合方法引用，有效地简化了代码并提高了可读性。

Predicate<Apple>是个谓词，代表一个方法，这个方法接收一个Apple类型的参数，返回布尔值，调用的时候将这样一个方法传给它就好了；
FilteringApples::isHeavyApple是方法引用的语法，读作“FilteringApples的isHeavyApple方法”，方法引用的出现使得方法可以当成值（变量，对象）被传递；

package _1._2._2;

import net.sf.json.JSONArray;
import net.sf.json.JSONObject;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.function.Predicate;

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 = filterApples(inventory, FilteringApples::isGreenApple);
        System.out.println(greenApples);

        // [Apple{color='green', weight=155}]
        List<Apple> heavyApples = filterApples(inventory, FilteringApples::isHeavyApple);
        System.out.println(heavyApples);
    }

    public static boolean isGreenApple(Apple apple) {
        return "green".equals(apple.getColor());
    }

    public static boolean isHeavyApple(Apple apple) {
        return apple.getWeight() > 150;
    }

    public static List<Apple> filterApples(List<Apple> inventory, Predicate<Apple> 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 +
                    '}';
        }
    }

}