title: about Java's classpath setting on Linux
body: <p>everyone.</p>
  
  <p>I used openjdk-7 on arch linux. I started to learn Java recently, and encountered such a problem:</p>
  
  <p>I created a file at /home/hqwrong/Code/java/mew/Mouth.java:</p>
  
  <pre><code>package mew;
  
  public class Mouth{
     public static void main(String argv[]){
         pickle.Say s = new pickle.Say();
    }
  }
  </code></pre>
  
  <p>and another one at /home/hqwrong/Code/java/pickle/Say.java :</p>
  
  <pre><code>package pickle;
  
  public class Say{
     public Say(){
        System.out.println("Say");
     }
  }
  </code></pre>
  
  <p>I compiled Say.java to Say.class,using:</p>
  
  <pre><code>$ cd /home/hqwrong/Code/java/pickle
  $ javac Say.java
  </code></pre>
  
  <p>which is successful.</p>
  
  <p>I compiled Mouth.java ,using:</p>
  
  <pre><code>$ cd ../mew
  $ export CLASSPATH=.:/home/hqwrong/Code/java/
  $ javac Say.java
  </code></pre>
  
  <p>no error message.</p>
  
  <p>But after I type:</p>
  
  <p>$ java Say</p>
  
  <p>I got:</p>
  
  <pre><code>Exception in thread "main" java.lang.SecurityException: Prohibited package name: java.mew
  at java.lang.ClassLoader.preDefineClass(ClassLoader.java:649)
  at java.lang.ClassLoader.defineClass(ClassLoader.java:785)
   at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
  at java.net.URLClassLoader.defineClass(URLClassLoader.java:449)
  at java.net.URLClassLoader.access$100(URLClassLoader.java:71)
  at java.net.URLClassLoader$1.run(URLClassLoader.java:361)
  at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
  at java.security.AccessController.doPrivileged(Native Method)
  at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
  at java.lang.ClassLoader.loadClass(ClassLoader.java:423)
  at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
  at java.lang.ClassLoader.loadClass(ClassLoader.java:356)
  at sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:472)
  </code></pre>
  
  <p>It's same when I use:</p>
  
  <pre><code>$ java -cp $CLASSPATH Say
  </code></pre>
  
  <p>I need your help,please?</p>