/**
* 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>

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>

/**
* 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;
  }
}

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>

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>