1. Create JFrame
2. Modify code this way (stupid way.This comment has no sense):
.
.
.
   /**
    private void exitForm(java.awt.event.WindowEvent evt) {
        System.exit (0);
    }
   */
    public static void main (String args[]) {
        new Visual ().show ();
    }
.
.
note: Comment body is in guarded block

3. Using PropertySheet Edit JavaDoc comment. Click OK button. You will see Error: Attempt to modify guarded block. It is correct, but look at code. You will see this:

   //** private void exitForm(java.awt.event.WindowEvent evt) {
     * System.exit (0);
     * }
     */**
    private void exitForm(java.awt.event.WindowEvent evt) {
        System.exit (0);
    }
   */
    public static void main (String args[]) {
        new Visual ().show ();
    }