为什么我这里Scanner类不能用啊?
											import java.util.*;
public class Ppt
{
       public static void main(String arg[])
        {
                Scanner sc = new Scanner(System.in);
                int i = sc.nextInt();
        }
}
为什么,我编译时会不行?
错误:
     Ppt.java:6: cannot resolve symbol
         symbol  : class Scanner
         location: class Ppt
                Scanner sc = new Scanner(System.in);
                ^
         Ppt.java:6: cannot resolve symbol
         symbol  : class Scanner
         location: class Ppt
                Scanner sc = new Scanner(System.in);
                                 ^

											