JAVA中Collections工具类sort()排序方法

发布时间：2020-12-14 14:45:09 所属栏目：Java 来源：网络整理

导读：本问介绍了Collections工具类两种sort()方法，具体如下：一、Collections工具类两种sort()方法格式一： public static T extends Comparable super T void sort(ListT list) 说明：该方法中的泛型T都是Comparable接口的子类，即只有是Comparable接口子类类

本问介绍了Collections工具类两种sort()方法，具体如下：

一、Collections工具类两种sort()方法

格式一： public static <T extends Comparable<? super T>> void sort(List<T> list)

说明：该方法中的泛型<T>都是Comparable接口的子类，即只有是Comparable接口子类类型的数据，才能进行比较排序。如果其他类型的数据要进行比较排序，必须继承Comparable接口并

覆写equals()和compareTo()方法。其中如String类、Integer类都是Comparable接口子类，可以进行排序，而基本类型不能进行sort排序。比较项目在类内指定

格式二：public static <T> void sort(List<T> list,Comparator<? super T> c)

说明：该方法中指定比较方式Comparator<? super T> c，即c必须实现Comparator<? super T>接口，覆写compareTo()方法指定比较项目。比较项目在类外指定，比较灵活

二、示例

示例中获取字符串和数字的公用方法：

/**
   * 生成随机 不重复的字符串 : number 生成字符串个数
   */
  public static List<String> generateString(int number) {
    List<String> listString = new ArrayList<>(); // 用于存放返回值
    List<Integer> length = null; // 字符串长度
    StringBuffer sb = new StringBuffer(); // 中间变量
    int control = 0; // 控制个数
    String[] chars = new String[] { "a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z","0","1","2","3","4","5","6","7","8","9","A","B","C","D","E","F","G","H","I","J","K","L","M","N","O","P","Q","R","S","T","U","V","W","X","Y","Z" };
    while (true) {
      // 控制结束
      if ( control==number ) {
        break;
      }
      // 生成随机数，生成36位的2aaab761-4341-4968-aceb-3861ee3824b2 UUID类型数据
      String uuid = UUID.randomUUID().toString().replace("-","");
      sb.setLength(0);
      // 获得随机字符串长度，长度不为0
      do {
        length = getDiffNo(1,11);
      } while ( length.get(0)==0 );
      // 拼凑字符串
      for (int i=0; i<length.get(0); i++) {
        String str = uuid.substring(i*3,(i*3+3));
        //将str字符串转换为16进制，获得其值
        int x = Integer.parseInt(str,16);
        //取余：x % 0x3E--0x3E = 3*16 + 14 = 62,其中chars有62个字符
        sb.append(chars[x % 0x3E]);
      }
      listString.add(sb.toString());
      control++;
    }
    return listString;
  }

  /**
   * 生成随机不重复的数字 :n生成个数 max生成范围
   */
  public static List<Integer> getDiffNo(int n,int max) {
    // 生成 [0-n] 个不重复的随机数
    // list 用来保存这些随机数
    List<Integer> list = new ArrayList<>();
    Random random = new Random();
    Integer k;
    for (int i=0; i<n; i++) {
      do {
        k = random.nextInt(max);
      } while (list.contains(k));
      list.add(k);
    }
    return list;
  }

1、对Integer泛型的List进行排序

/**
   * 1.通过Collections.sort()方法，对Integer泛型的List进行排序；
   * 创建一个Integer泛型的List，插入十个100以内的不重复随机整数， 调用Collections.sort()方法对其进行排序
   * 2.排序规则：先数字后字母，数字0-9，字母A-Z a-z的顺序
   */
  public void listIntegerSort() {
    // 插入十个100以内的不重复随机整数
    List<Integer> integerList = getDiffNo(10,100);
    System.out.println("-------------排序前--------------");
    for (Integer integer : integerList) {
      System.out.println("元素：" + integer);
    }
    Collections.sort(integerList);
    System.out.println("----------------排序后-------------------");
    for (Integer integer : integerList) {
      System.out.println("元素：" + integer);
    }
  }

2、对String泛型的List进行排序

/**
   * 1.对String泛型的List进行排序； 创建String泛型的List，添加乱序的String元素，
   * 调用sort方法，再次输出排序后的顺序
   */
  public void listStringSort() {
    List<String> stringList = new ArrayList<String>();
    stringList.add("eipJlcx");
    stringList.add("WvQRufC");
    stringList.add("J");
    stringList.add("HdaU2G");
    stringList.add("M0WswHD3");
    System.out.println("------------排序前-------------");
    for (String string : stringList) {
      System.out.println("元素：" + string);
    }
    Collections.sort(stringList);
    System.out.println("--------------排序后---------------");
    for (String string : stringList) {
      System.out.println("元素：" + string);
    }
  }

/**
   * 对String泛型的List进行排序，要求随机生成10个的不重复字符串，字符串的长度在10以内
   */
  public void listStringRandomSort() {
    // 生成随机字符串
    List<String> listString = generateString(10);
    System.out.println("--------------排序前---------------");
    for (String integer : listString) {
      System.out.println("元素：" + integer);
    }
    // 排序
    Collections.sort(listString);
    System.out.println("----------------排序后------------------");
    for (String integer : listString) {
      System.out.println("元素：" + integer);
    }
  }

3、对其他类型泛型的List进行排序

Course类实现

/**
 * 课程类
 * @author Administrator
 *
 */
public class Course {
  public String id;
  public String name;
  public Course(String id,String name) {
    this.id = id ;
    this.name = name;
  }
  public Course() {
  }
  
  @Override
  public int hashCode() {
    final int prime = 31;
    int result = 1;
    result = prime * result + ((name == null) ? 0 : name.hashCode());
    return result;
  }

  @Override
  public boolean equals(Object obj) {
    if (this == obj)
      return true;
    if (obj == null)
      return false;
    if (!(obj instanceof Course))
      return false;
    Course other = (Course) obj;
    if (name == null) {
      if (other.name != null)
        return false;
    } else if (!name.equals(other.name))
      return false;
    return true;
  }
}

Student类实现Comparable接口，类内设置比较项

import java.util.HashSet;
import java.util.Set;

/**
 * 学生类
 * @author Administrator
 *
 */
public class Student implements Comparable<Student> {
  public String id;
  public String name;
  public Set<Course> courses;
  
  public Student(String id,String name) {
    this.id = id;
    this.name = name;
    this.courses = new HashSet<Course>();
  }

  @Override
  public int hashCode() {
    final int prime = 31;
    int result = 1;
    result = prime * result + ((name == null) ? 0 : name.hashCode());
    return result;
  }

  @Override
  public boolean equals(Object obj) {
    if (this == obj)
      return true;
    if (obj == null)
      return false;
    if (!(obj instanceof Student))
      return false;
    Student other = (Student) obj;
    if (name == null) {
      if (other.name != null)
        return false;
    } else if (!name.equals(other.name))
      return false;
    return true;
  }

  @Override
  public int compareTo(Student o) { // 设置ID为比较项
    // TODO Auto-generated method stub
    return this.id.compareTo(o.id);
  }
}

实现Comparator接口，类外设置比较项

import java.util.Comparator;
public class StudentComparator implements Comparator<Student> {

  @Override
  public int compare(Student o1,Student o2) {
    // TODO Auto-generated method stub
    return o1.name.compareTo(o2.name);
  }
}

比较Student类

/**
   * 对其他类型泛型的List进行排序，以Student为例。
   */
  public void listComparatorSort() {
    List<Student> studentList = new ArrayList<Student>();
    List<Integer> list = getDiffNo(4,1000);

    studentList.add(new Student(list.get(0) + "","Mike"));
    studentList.add(new Student(list.get(1) + "","Angela"));
    studentList.add(new Student(list.get(2) + "","Lucy"));
    studentList.add(new Student(1000 + "","Beyonce"));
    System.out.println("--------------排序前---------------");
    for (Student student : studentList) {
      System.out.println("学生：" + student.id + ":" + student.name);
    }
    // 实现Comparator<T>接口，设置ID比较方式
    Collections.sort(studentList);
    System.out.println("----------------按照ID排序后------------------");
    for (Student student : studentList) {
      System.out.println("学生：" + student.id + ":" + student.name);
    }

    // 实现Comparator<T>接口，设置特定比较方式，以name比较排序
    Collections.sort(studentList,new StudentComparator());
    System.out.println("----------------按照姓名排序后-----------------");
    for (Student student : studentList) {
      System.out.println("学生：" + student.id + ":" + student.name);
    }
  }

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持编程小技巧。

（编辑：李大同）

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