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 ~]$