Comparator的传统和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的类 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，匿名内部类直接对象字段比较排序 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直接对象字段比较排序 Collections.sort(students, ( Student o1,Student o2)->{ return o1.getAge().compareTo(o2.getAge()); }); System.out.println(students); */

/* //用法三，Lambda直接对象字段比较排序，声明类型去掉,JVM会自动去找对应类型方法 Collections.sort(students, (o1,o2)->{ return o1.getAge().compareTo(o2.getAge()); }); System.out.println(students); */

/* //用法四，Lambda，静态方法调用--Student::compareAgeStatic语法的意思是调用Student的compareAgeStatic方法 //,我们ctrl+鼠标左点下compareAgeStatic可跳到compareAgeStatic方法如下： // public static int compareAgeStatic(Student s1, Student s2){ // return s1.getAge().compareTo(s2.getAge()); // } //可以看出其实就是用法三的简写

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

*/

//用法五，Lambda，非静态方法调用--参考方法4，原理一模一样 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 + + }; } }