1.2.3 从传递方法到Lambda表达式

• Lambda表达式又叫匿名方法，省去只用一次的短方法的定义；
• 具体什么时候用Lambda表达式，怎么用，以代码的清晰度为准绳；

package _1._2._3;

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 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 greenApples2 = filterApples(inventory, (Apple a) -> "green".equals(a.getColor()));
        System.out.println(greenApples2);

        // [Apple{color='green', weight=155}]
        List heavyApples2 = filterApples(inventory, (Apple a) -> a.getWeight() > 150);
        System.out.println(heavyApples2);

        // []
        List weirdApples = filterApples(inventory, (Apple a) -> a.getWeight() < 80 ||
                "brown".equals(a.getColor()));
        System.out.println(weirdApples);
    }

    public static List filterApples(List inventory, Predicate p){
        List 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 +
                    '}';
        }
    }

}