title: Error: Could not find or load main class sun.applet.AppletViewer. Caused by: java.lang.ClassNotFoundException: sun.applet.AppletViewer
body: <p>I'm trying to write some simple codes from the book <strong>The Art and Science of Java</strong>. As an example, I am writing the codes of <code>Liftoff</code> but I get the same error every time I write <code>extends ConsoleProgram</code>.</p>
  
  <pre><code>import acm.program.*;
  
  public class Countdown extends ConsoleProgram {
  
      public void run() {
          for (int t = START; t &gt;= 0; t--) {
              println(t);
          }
  
          println("Liftoff!");
      }
  
      private static final int START = 10;
  }
  </code></pre>
  
  <p>I expect the output:</p>
  
  <pre><code>10
  9
  8
  7
  6
  5
  4
  3
  2
  1
  Liftoff
  </code></pre>