我试了，第三个可以啊[atp@gateway ~]$ cat aaa.java import java.util.Vector; public class aaa { 　　public static void main (String [] s) 　　{ 　　　　Vector a = new Vector(); 　　　　a.add("hi"); 　　　　Vector b = (Vector)a.clone(); 　　　　System.out.println(b); 　　} } [atp@gateway ~]$ javac aaa.java Note: aaa.java uses unchecked or unsafe operations. Note: Recompile with -Xlint:unchecked for details. [atp@gateway ~]$ java aaa [hi] [atp@gateway ~]$　

what is Vector for?Vector[]? (more...)

Leave itthis warning message just shows that compiler cannot assure correctness of this casting operation as clone() method returns type of object. It is really programmer's responsibility to avoid any casting failure.