title: Error when generating JNI header file
body: <p>I'm trying to generate the JNI header file through command line. when I 
  typed javah myclass.class, the errors was </p>
  
  <pre><code>Exception in thread main java.IllegalArgumentException: not a valid class name
  at com.sun.tools.javac.api.JavacTool.getTask&lt;JavacTool.java:177&gt;
  at com.sun.tools.javac.api.JavacTool.getTask&lt;JavacTool.java:68&gt;
  at com.sun.tools.javah.api.JavachTask.run&lt;JavahTask.java:509&gt;
  at com.sun.tools.javah.api.JavachTask.run&lt;JavahTask.java:335&gt;
  at com.sun.tools.javah.Main.main&lt;Main.java:46&gt;
  </code></pre>
  
  <p>but when I typed javah myclass</p>
  
  <p>Error:could not find class file for 'myclass'</p>
  
  <p>Previously, when  I typed ls in the my class directory, the class file was exist.</p>
  
  <p>this is my snippet codes </p>
  
  <pre><code>package com.blablabla
  
  public static native long myclass(long n);
  </code></pre>
  
  <p>Does anybody know how to solve this issue?</p>
  
  <p>thanks</p>