达人们帮我看看问题在哪里

import java.io.FileInputStream;
import java.io.InputStream;
public class WriteExcel{
public WriteExcel(){
try{
InputStream is = new FileInputStream("D:\\mm.xls");
jxl.Workbook rwb = jxl.Workbook.getWorkbook(is);
}catch (Exception e){
e.printStackTrace();
}
}
public static void main(String[] arg){
try{
WriteExcel w = new WriteExcel();
}catch(Exception e){
e.getMessage();
}
}
}

Exception in thread "main" java.lang.NoClassDefFoundError: jxl/Workbook
at WriteExcel.<init>(WriteExcel.java:13)
at WriteExcel.main(WriteExcel.java:22)

cd 到你的目录下
javac -d . *.java
搞定

jxl.Workbook 是什么啊,不懂

编译已经通过了