方法引用

package com.example.demo;

import java.time.LocalDate;

class Person {

    public Person(String name, LocalDate birthday) {
        this.name = name;
        this.birthday = birthday;
    }

    String name;
    LocalDate birthday;

    public LocalDate getBirthday() {
        return birthday;
    }

    public static int compareByAge(Person a, Person b) {
        return a.birthday.compareTo(b.birthday);
    }

    @Override
    public String toString() {
        return this.name;
    }

}

package com.example.demo;

import org.junit.jupiter.api.Test;
import org.springframework.boot.test.context.SpringBootTest;

import java.time.LocalDate;
import java.util.Arrays;
import java.util.Comparator;

@SpringBootTest
class DemoApplicationTests {

    @Test
    public void test() { //匿名内部类写法
        Person[] pArr = new Person[]{
                new Person("003", LocalDate.of(2020,9,1)),
                new Person("001", LocalDate.of(2020,2,1)),
                new Person("002", LocalDate.of(2020,3,1)),
                new Person("004", LocalDate.of(2020,12,1))};

        // 使用匿名类
        Arrays.sort(pArr, new Comparator<Person>() {
            @Override
            public int compare(Person a, Person b) {
                return a.getBirthday().compareTo(b.getBirthday());
            }
        });
        System.out.println(Arrays.asList(pArr));
    }

    @Test
    public void Test1() {   //使用Lambda表达式，调用已存在的方法
        Person[] pArr = new Person[]{
                new Person("003", LocalDate.of(2020,9,1)),
                new Person("001", LocalDate.of(2020,2,1)),
                new Person("002", LocalDate.of(2020,3,1)),
                new Person("004", LocalDate.of(2020,12,1))};

        //使用lambda表达式和类的静态方法
        Arrays.sort(pArr, (a , b) -> Person.compareByAge(a, b));
        System.out.println(Arrays.asList(pArr));
    }

    @Test
    public void test2() {  //使用Lambda表达式，调用已存在的方法
        Person[] pArr = new Person[]{
                new Person("003", LocalDate.of(2020,9,1)),
                new Person("001", LocalDate.of(2020,2,1)),
                new Person("002", LocalDate.of(2020,3,1)),
                new Person("004", LocalDate.of(2020,12,1))};

        //使用lambda表达式和类的静态方法
        Arrays.sort(pArr, (a ,b) -> Person.compareByAge(a, b));
        System.out.println(Arrays.asList(pArr));
    }

    @Test
    void Test3() {       //使用方法引用
        Person[] pArr = new Person[]{
                new Person("003", LocalDate.of(2020,9,1)),
                new Person("001", LocalDate.of(2020,2,1)),
                new Person("002", LocalDate.of(2020,3,1)),
                new Person("004", LocalDate.of(2020,12,1))};

        //使用lambda表达式和类的静态方法
        Arrays.sort(pArr, Person::compareByAge);
        System.out.println(Arrays.asList(pArr));
    }

}