import java.util.*;
public class TestComparable{
  public static void main(String args[]){
    List l = new ArrayList();
    l.add(new testname("Giggs","wong") );
    l.add(new testname("beckham","li") );
    l.add(new testname("jack","chen") );
    l.add(new testname("suki","xu") );
    Collections.reverse(l);
    System.out.println(l);
    Collections.sort(l);                 // 排序testname 类  // 怎么老出现异常 
    System.out.println(l);
  }
}
class testname{
  public String firstname;
  public String lastname;
  testname(String f,String l){
    firstname = f;
    lastname = l;
  }
  public int compareTo(Object o){
     testname t = (testname) o;
     int bo = (t.lastname);
     return ( bo !=0 ? bo : (t.firstname) );

 
  }
    


  public String toString(){
    return lastname+" "+firstname;
  }

}

Exception in thread "main" java.lang.ClassCastException: testname cannot be cast
 to java.
        at java.(ComparableTimSor
t.java:290)
        at java.(ComparableTimSort.java:157)
        at java.(ComparableTimSort.java:146)
        at java.util.Arrays.sort(Arrays.java:472)
        at java.util.Collections.sort(Collections.java:155)
        at TestComparable.main(TestComparable.java:11)
异常代码   到底什么意思??

sort（）的作用是根据自然顺序对列表进行排序，这个排序动作的前提条件是，你List集合立的元素是可以排序的才行，如果不能排序，比如说是字符串之类，那就要抛出你看见的异常了。

收到的鲜花

• 灵想 于 2013-07-31 23:16 送鲜花  3朵   附言：感谢

我这程序弄好了 ..  原来要写成  class testname implements Comparable
字符串不能排序么  String类本身不是也实现了Comparable接口吗