对ArrayList中的元素进行排序的几种方式

一、使用Collections工具类

1、对基本类型排序

通过Collections.sort()对基本类型排序默认是以升序排序

// 1.Collections.sort()默认按照升序排序
List<Integer> integerList = new ArrayList<>();
Collections.addAll(integerList,1,2,6,5,5,4,55,4,5,5,4,5,2,4,6,2,45);
Collections.sort(integerList);
System.out.println(integerList);

2、对字符串类型排序

对字符串类型排序默认按照首字母a-z排序

// 2.对字符串类型排序
List<String> strings = new ArrayList<>();
Collections.addAll(strings,"d","gsf","trh","fsd","an");
Collections.sort(strings);
System.out.println(strings);

3、对对象排序

如何使用Collections对对象排序呢？

其实只需要让我们的数据类型实现Comparable接口即可，下面定义一个实现Comparable接口的学生类，并且实现compareTo方法，让学生类只比较年龄。

/**
 * 学生
 *
 * @author ez4sterben
 * @date 2023/07/18
 */
public class Student implements Comparable<Student> {

    private String id;
    private String name;
    private Integer age;
    private String sex;

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

    public Student(Integer age) {
        this.age = age;
    }

    public String getId() {
        return id;
    }

    public void setId(String 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;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    @Override
    public int compareTo(Student o) {
    	// 这种是升序
        return this.getAge() - o.getAge();
        // 这种是降序
        // return o.getAge() - this.getAge();
    }
}

排序方法和正常使用一样，直接把整个list传入即可

// 3.对对象排序
        List<Student> students = new ArrayList<>();
        Collections.addAll(students,
                new Student(18),
                new Student(26),
                new Student(20),
                new Student(16),
                new Student(12));
        System.out.println(students);
        Collections.sort(students);
        System.out.println(students);

二、使用stream流

// 2.lambda表达式
        Stream<Integer> sorted = integerList.stream().sorted();
        System.out.println(Arrays.toString(sorted.toArray()));

三、使用排序算法（以冒泡排序为例）

// 3.直接使用排序算法（以冒泡排序为例）
        for(int i = 0; i < integerList.size() - 1; i++){
            for(int j = 0; j < integerList.size() - i - 1; j++){
                if(integerList.get(j) > integerList.get(j + 1)){
                    Integer temp = integerList.get(j);
                    integerList.set(j, integerList.get(j + 1));
                    integerList.set(j + 1, temp);
                }
            }
        }
        System.out.println(integerList);

四、测试类整体代码

import java.util.*;
import java.util.stream.Stream;

/**
 * 数组列表排序
 *
 * @author ez4sterben
 * @date 2023/07/19
 */
public class ArrayListSort {
    public static void main(String[] args) {
        List<Integer> integerList = new ArrayList<>();
        Collections.addAll(integerList,1,2,6,5,5,4,55,4,5,5,4,5,2,4,6,2,45);
        // 1.Collections.sort()默认按照升序排序
        Collections.sort(integerList);
        System.out.println(integerList);
        // 2.对字符串类型排序
        List<String> strings = new ArrayList<>();
        Collections.addAll(strings,"d","gsf","trh","fsd","an");
        Collections.sort(strings);
        System.out.println(strings);
        // 3.对对象排序
        List<Student> students = new ArrayList<>();
        Collections.addAll(students,
                new Student(18),
                new Student(26),
                new Student(20),
                new Student(16),
                new Student(12));
        System.out.println(students);
        Collections.sort(students);
        System.out.println(students);

        // 2.lambda表达式
        Stream<Integer> sorted = integerList.stream().sorted();
        System.out.println(Arrays.toString(sorted.toArray()));

        // 3.直接使用排序算法（以冒泡排序为例）
        for(int i = 0; i < integerList.size() - 1; i++){
            for(int j = 0; j < integerList.size() - i - 1; j++){
                if(integerList.get(j) > integerList.get(j + 1)){
                    Integer temp = integerList.get(j);
                    integerList.set(j, integerList.get(j + 1));
                    integerList.set(j + 1, temp);
                }
            }
        }
        System.out.println(integerList);

    }
}