JAVA中Collections工具类sort()排序方法

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 > void sort(List list)

说明：该方法中的泛型都是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 void sort(List list, Comparator c)

说明：该方法中指定比较方式Comparator c，即c必须实现Comparator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：

  public static List generateString(int number) {
    List listString = new ArrayList<>(); // 用于存放返回值
    List 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 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 list = new ArrayList<>();
    Random random = new Random();
    Integer k;
    for (int i=0; i

1、对Integer泛型的List进行排序




  public void listIntegerSort() {
    // 插入十个100以内的不重复随机整数
    List 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




  public void listStringSort() {
    List stringList = new ArrayList();
    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);
    }
  }




  public void listStringRandomSort() {
    // 生成随机字符串
    List 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




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;


public class Student implements Comparable {
  public String id;
  public String name;
  public Set courses;
  
  public Student(String id, String name) {
    this.id = id;
    this.name = name;
    this.courses = new HashSet();
  }

  @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 {

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



比较Student类




  public void listComparatorSort() {
    List studentList = new ArrayList();
    List 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);
    }
  }



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