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[Java教程]JAVA Collections工具类sort()排序方法

主要分析内容:

一、Collections工具类两种sort()方法

二、示例

 

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);    }  }

 

参考学习连接:

Comparable接口的实现和使用:http://www.cnblogs.com/gnuhpc/archive/2012/12/17/2822251.html

Collections.sort对List排序的两种方法:http://blog.csdn.net/wxx614817/article/details/50628197