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Java中Collections类的排序sort函数两种用法 (转http://viver120.blog.163.com/blog/static/60072482013010111228695/)

java中的Colletions类主要实现列表List的排序功能。根据函数参数的传递,具体的排序可以分为 :

1.  自然排序(natural ordering)。

函数原型:sort(List<T> list)
说明:参数是要参与排序列表的List对象                                                               
实例说明:参与排序的列表的元素Student必须实现Comparable接口的
public int compareTo(Object o) 方法,在里面写对比的原则。
然后调用Colletions.sort(排序对象的列表)    
请看如下示例:

import java.util.ArrayList;import java.util.Arrays;import java.util.Collection;import java.util.Collections;import java.util.Iterator;import java.util.List;class ArrayListTest{public static void printElements(Collection c){  Iterator it = c.iterator();  while(it.hasNext()){  System.out.println(it.next());}}public static void main(String[] args){  ArrayList<Student> al = new ArrayList<Student>();  al.add(new Student(2,"aora"));  al.add(new Student(1,"longyu"));  al.add(new Student(3,"goso"));  Collections.sort(al);  printElements(al);}}class Student implements Comparable{  int num;  String name;  Student(int num,String name){  this.num = num;  this.name = name;}  public int compareTo(Object o) {    Student s = (Student)o;    return num > s.num ? 1 : (num == s.num ? 0 : -1);  };  public String toString(){    return "num = " + this.num + ",name = " + this.name;  } }

2.  实现比较器(Comparator)接口。

函数原型:sort(List<T> list, Comparator<? super T> c)
说明:第一个参数同左,第二个参数是构建对比规则的对比器Comparator。
实例说明(如下):在参与排序的列表的元素Student中写一个内部类作为
Student的对比器,这个对比器要实现Comparator接口的public int compare(Object o1,
Object o2)方法,然后调用Colletions.sort(排序对象的列表,对比器)  

请看如下示例:

 1 import java.util.ArrayList; 2 import java.util.Collection; 3 import java.util.Collections; 4 import java.util.Iterator; 5 import java.util.Comparator;
6 class ArrayListTest{ 7   public static void printElements(Collection c){ 8     Iterator it = c.iterator(); 9     while(it.hasNext()){10       System.out.println(it.next());11     }12   }
13   public static void main(String[] args){14     ArrayList<Student> al = new ArrayList<Student>();15     al.add(new Student(2,"qingan"));16     al.add(new Student(1,"longyu"));17     al.add(new Student(3,"goso"));18     al.add(new Student(2,"aora"));19     Collections.sort(al,new Student.studentComparator());20     printElements(al);21    }22 }
23 class Student{24   int num;25   String name;26   Student(int num,String name){27     this.num = num;28     this.name = name;29   }30   static class studentComparator implements Comparator{31     public int compare(Object o1,Object o2){32       Student s1 = (Student)o1;33       Student s2 = (Student)o2;34       int result = s1.num > s2.num ? 1 : (s1.num == s2.num ? 0 : -1);35 // 注意:此处在对比num相同时,再按照name的首字母比较。36       if(result == 0){37         result = s1.name.compareTo(s2.name);38       }39       return result;40     } 41 } 42   public String toString(){43     return "num = " + this.num + ",name = " + this.name;44   } 45 }

 

Java中Collections类的排序sort函数两种用法 (转http://viver120.blog.163.com/blog/static/60072482013010111228695/)