【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？

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。

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;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);    }}

来源地址：https://blog.csdn.net/qq_51383106/article/details/131814255