title: Eclipse doesn't compile java files into classes
body: <p>I have no idea why, but from today Eclipse doesn't compile .java files into .class. I press the "Run" button and Eclipse only tries to run the program rather then compiles it first, so i get this error all the time:</p>
  
  <pre><code>Exception in thread "main" java.lang.NoClassDefFoundError
  </code></pre>