【java】对ArrayList中的元素进行排序的几种方式

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 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 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 {

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 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 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 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 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 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 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);

}

}