List对象集合排序

实体类

package com.ledao.entity;

/**
 * 学生实体类
 *
 * @author LeDao
 * @company
 * @create 2021-11-21 23:19
 */
public class Student {

    /**
     * 编号
     */
    private Integer id;
    /**
     * 姓名
     */
    private String name;
    /**
     * 年龄
     */
    private Integer age;

    public Student() {
    }

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

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }

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

排序

Collections.sort

该方法有两个参数，参数一为要排序的对象集合，参数二为比较器

import com.ledao.entity.Student;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

/**
 * @author LeDao
 * @company
 * @create 2021-11-22 20:43
 */
public class Test {

    public static void main(String[] args) {

        List<Student> studentList = new ArrayList<>(16);
        studentList.add(new Student(2, "atn", 14));
        studentList.add(new Student(1, "tom", 12));
        studentList.add(new Student(3, "bob", 11));
        studentList.add(new Student(5, "alex", 13));
        Collections.sort(studentList, new Comparator<Student>() {
            @Override
            public int compare(Student o1, Student o2) {
                return o1.getAge()-o2.getAge();
            }
        });
        for (Student student : studentList) {
            System.out.println(student.getId()+","+student.getName()+","+student.getAge());
        }
    }
}

List.sort

方法参数为比较器

import com.ledao.entity.Student;

import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;

/**
 * @author LeDao
 * @company
 * @create 2021-11-22 20:43
 */
public class Test {

    public static void main(String[] args) {

        List<Student> studentList = new ArrayList<>(16);
        studentList.add(new Student(2, "atn", 14));
        studentList.add(new Student(1, "tom", 12));
        studentList.add(new Student(3, "bob", 11));
        studentList.add(new Student(5, "alex", 13));
        studentList.sort(new Comparator<Student>() {
            @Override
            public int compare(Student o1, Student o2) {
                return o1.getAge() - o2.getAge();
            }
        });
        for (Student student : studentList) {
            System.out.println(student.getId()+","+student.getName()+","+student.getAge());
        }
    }
}

Stream流操作

通过Stream流操作会返回一个新的并且经过排序的List集合，具体步骤为：①创建要排序集合的流 ②进行排序 ③生成新集合

import com.ledao.entity.Student;

import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
import java.util.stream.Collectors;

/**
 * @author LeDao
 * @company
 * @create 2021-11-22 20:43
 */
public class Test {

    public static void main(String[] args) {

        List<Student> studentList = new ArrayList<>(16);
        studentList.add(new Student(2, "atn", 14));
        studentList.add(new Student(1, "tom", 12));
        studentList.add(new Student(3, "bob", 11));
        studentList.add(new Student(5, "alex", 13));
        List<Student> resultList=studentList.stream().sorted(new Comparator<Student>() {
            @Override
            public int compare(Student o1, Student o2) {
                return o1.getId()-o2.getId();
            }
        }).collect(Collectors.toList());
        for (Student student : resultList) {
            System.out.println(student.getId()+","+student.getName()+","+student.getAge());
        }
    }
}

实体类实现Comparable接口

实体类实现Comparable接口的compareTo方法，然后再使用Collections.sort方法（参数只有一个：要排序的集合）

实体类

package com.ledao.entity;

/**
 * 学生实体类
 *
 * @author LeDao
 * @company
 * @create 2021-11-21 23:19
 */
public class Student implements Comparable<Student>{

    /**
     * 编号
     */
    private Integer id;
    /**
     * 姓名
     */
    private String name;
    /**
     * 年龄
     */
    private Integer age;

    public Student() {
    }

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

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }

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

    @Override
    public int compareTo(Student o) {
        return o.getId()-this.getId();
    }
}

测试方法

import com.ledao.entity.Student;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.stream.Collectors;

/**
 * @author LeDao
 * @company
 * @create 2021-11-22 20:43
 */
public class Test {

    public static void main(String[] args) {

        List<Student> studentList = new ArrayList<>(16);
        studentList.add(new Student(2, "atn", 14));
        studentList.add(new Student(1, "tom", 12));
        studentList.add(new Student(3, "bob", 11));
        studentList.add(new Student(5, "alex", 13));
        Collections.sort(studentList);
        for (Student student : studentList) {
            System.out.println(student.getId()+","+student.getName()+","+student.getAge());
        }
    }
}