用Java集合中的Collections.sort方法对list排序的两种方法

用Collections.sort方法对list排序有两种方法
第一种是list中的对象实现Comparable接口，如下：

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/** * 根据order对User排序 */ public class User implements Comparable                                  <user>                                       {     private String name;     private Integer order;     public String getName() {         return name;     }     public void setName(String name) {         this.name = name;     }     public Integer getOrder() {         return order;     }     public void setOrder(Integer order) {         this.order = order;     }     public int compareTo(User arg0) {         return this.getOrder().compareTo(arg0.getOrder());     } }                                  </user>

测试一下：

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public class Test{       public static void main(String[] args) {         User user1 = new User();         user1.setName("a");         user1.setOrder(1);         User user2 = new User();         user2.setName("b");         user2.setOrder(2);         List                                  <user>                                        list = new ArrayList                                       <user>                                            ();         //此处add user2再add user1         list.add(user2);         list.add(user1);         Collections.sort(list);         for(User u : list){             System.out.println(u.getName());         }     } }                                       </user>                                  </user>

输出结果如下 
a
b 
第二种方法是根据Collections.sort重载方法来实现，例如：

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/** * 根据order对User排序 */ public class User { //此处无需实现Comparable接口     private String name;     private Integer order;     public String getName() {         return name;     }     public void setName(String name) {         this.name = name;     }     public Integer getOrder() {         return order;     }     public void setOrder(Integer order) {         this.order = order;     } }

主类中这样写即可：

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public class Test{     public static void main(String[] args) {         User user1 = new User();         user1.setName("a");         user1.setOrder(1);         User user2 = new User();         user2.setName("b");         user2.setOrder(2);         List                                  <user>                                        list = new ArrayList                                       <user>                                            ();         list.add(user2);         list.add(user1);                   Collections.sort(list,new Comparator                                            <user>                                                 (){             public int compare(User arg0, User arg1) {                 return arg0.getOrder().compareTo(arg1.getOrder());             }         });         for(User u : list){             System.out.println(u.getName());         }     } }                                            </user>                                       </user>                                  </user>

输出结果如下 
a
b 
前者代码结构简单，但是只能根据固定的属性排序，后者灵活，可以临时指定排序项，但是代码不够简洁

多字段的场合：

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Collections.sort(list,new Comparator                                       <user>                                            (){             public int compare(User arg0, User arg1) {  //            第一次比较专业                 int i = arg0.getOrder().compareTo(arg1.getOrder());   //            如果专业相同则进行第二次比较             if(i==0){ //                第二次比较                 int j=arg0.getXXX().compareTo(arg1.getXXX()); //                如果学制相同则返回按年龄排序                 if(j==0){                     return arg0.getCCC().compareTo(arg1.getCCC());                 }                 return j;             }             return i;             }         });                                       </user>