title: Java: why Observer is NOT an interface
body: <pre><code>import java.util.*;
  import java.awt.*;
  import java.awt.event.*;
  import java.applet.Applet;
  
  class Client extends Button implements Observer, ActionListener{
  ...
  }
  </code></pre>
  
  <p>with the code above, when i try to compile it with jdk (v 1.7.0_17) i get the following error:</p>
  
  <pre><code>error: interface expected here
  class Client extends Button implements Observer, ActionListener{
                                         ^
  </code></pre>
  
  <p>while on other computers it works (I've only checked it on 2 different linuxes) just fine.
  I'm using Windows 7 Professional 64-bit.</p>