【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<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？

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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;@Overridepublic 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;}@Overridepublic 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);

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二、使用stream流

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

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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);

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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);}
}