方法引用构造函数引用

Posted 2021-03-02 fly-book

import java.util.Arrays;
import java.util.List;

import static java.util.Comparator.comparing;

/**
 * 方法引用
 */
public class Quote{
    public static void main(String[] args){
        List<Apple> list = Arrays.asList(new Apple("red",120),new Apple("green",100));
        list.sort(comparing(Apple::getWeight));
        System.out.println(list);

        List<String> str = Arrays.asList("a","b","A","B");
//        str.sort((s1,s2)->s1.compareToIgnoreCase(s2));
        str.sort(String::compareToIgnoreCase);
        System.out.println(str);

    }
}

构造函数引用

public class Apple {
    private String color;
    private int weight;

    public Apple() {
    }

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

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

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

    public int getWeight() {
        return weight;
    }

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

    public String getColor() {
        return color;
    }

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

    @Override
    public String toString() {
        return "Apple{" +
                "color=‘" + color + ‘‘‘ +
                ", weight=" + weight +
                ‘}‘;
    }
}

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.function.BiFunction;
import java.util.function.Function;
import java.util.function.Supplier;

/**
 * @FunctionalInterface
 * public interface Supplier<T> {
 *      T get();
 * }
 */
public class Demo {
    public static List<Apple> map(List<Integer> list,Function<Integer,Apple> f){
        List<Apple> res = new ArrayList<>();
        for (Integer e : list) {
            res.add(f.apply(e));
        }
        return res;
    }

    public static void main(String[] args){
        /**
         * 等价于
         *  Supplier<Apple> c2 = () -> new Apple();
         *  Apple apple = c2.get();
         */
        Supplier<Apple> c1 = Apple::new;
        Apple apple = c1.get();


        /**
         * 等价于
         * Function<String,Apple> c2 = Apple::new;
         *  Apple a2 = c2.apply("red");
         */
        Function<String,Apple> c2 = Apple::new;
        Apple a2 = c2.apply("red");

        //传递给了Apple的构造函数
        List<Integer> weights = Arrays.asList(1,3,4,2,5);
        List<Apple> apples = map(weights,Apple::new);
        System.out.println(apples);

        /**
         * 等价于
         * BiFunction<String,Integer,Apple> c3 = (color,weight) -> new Apple(color,weight);
         * Apple a3 = c3.apply("green",110);
         */
        //具有两个参数的构造函数Apple(String color, Integer weight)
        BiFunction<String,Integer,Apple> c3 = Apple::new;
        Apple a3 = c3.apply("red",110);
        System.out.println(a3);



    }
}