Comparator的傳統和Lambda用法

DEMO1.java

package com.xiangshuai.lambda;

import java.nio.file.DirectoryStream;
import java.util.*;
//此包下提供了不少可以自由Lambda的類
import java.util.function.*;

/**
 * @author lqx
 * @ClassName DEMO1
 * @description  排序之Lambda
 * @date 2020/6/20 17:11
 */
public class DEMO1 {
    public static void main(String[] args) {
          List<Student> students=new ArrayList<>();
          students.add(new Student(10,"小明","ss"));
          students.add(new Student(30,"小明","ss"));
          students.add(new Student(20,"小明","ss"));
          students.add(new Student(90,"小明","ss"));
          students.add(new Student(200,"小明","ss"));
          students.add(new Student(80,"小明","ss"));
          students.add(new Student(1,"小明","ss"));
   /*
          //用法一，匿名內部類直接對象字段比較排序
          Collections.sort(students, new Comparator<Student>() {
              @Override
              public int compare(Student o1, Student o2) {
                  return o1.getAge().compareTo(o2.getAge());
              }
          });
        System.out.println(students);
   */

/*
   //用法二，Lambda直接對象字段比較排序
        Collections.sort(students, ( Student o1,Student o2)->{
            return  o1.getAge().compareTo(o2.getAge());
        });
         System.out.println(students);
        */

 /*
      //用法三，Lambda直接對象字段比較排序，聲明類型去掉,JVM會自動去找對應類型方法
      Collections.sort(students, (o1,o2)->{
            return  o1.getAge().compareTo(o2.getAge());
        });
        System.out.println(students);
        */

  /*
      //用法四，Lambda，靜態方法調用--Student::compareAgeStatic語法的意思是調用Student的compareAgeStatic方法
      //,我們ctrl+鼠標左點下compareAgeStatic可跳到compareAgeStatic方法如下：
       // public static int compareAgeStatic(Student s1, Student s2){
      //  return s1.getAge().compareTo(s2.getAge());
      // }
      //可以看出其實就是用法三的簡寫

       Collections.sort(students, Student::compareAgeStatic);
        System.out.println(students);

        */

        //用法五，Lambda，非靜態方法調用--參考方法4，原理一模一樣
      Collections.sort(students, Student::compareAge);
        System.out.println(students);

    }

}
 

Student.java

package com.xiangshuai.lambda;

/**
 * @author lqx
 * @ClassName Student
 * @description
 * @date 2020/6/21 12:19
 */
public class Student {
    private Integer age;
    private String name;
    private String address;

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public static int compareAge(Student s1, Student s2){
        return s1.getAge().compareTo(s2.getAge());
    }

    public static int compareAgeStatic(Student s1, Student s2){
        return  s1.getAge().compareTo(s2.getAge());
    }

    public Student(Integer age, String name, String address) {
        this.age = age;
        this.name = name;
        this.address = address;
    }

    public Student() {
    }

    @Override
    public String toString() {
        return "Student{" +
                "age=" + age +
                ", name='" + name + '\'' +
                ", address='" + address + '\'' +
                '}';
    }
}