/** Implementing the action of opening the about window. */
 public void aboutMenuItem_actionPerformed(ActionEvent e) {
   if (aboutWindow != null) aboutWindow.setVisible(true);
 }
 public void setAboutFileName(String fileName) {
   aboutWindow = new HTMLViewFrame(fileName);
   aboutWindow.setSize(450, 420);
 }
 /** Implementing the action of opening the usage window. */
 public void usageMenuItem_actionPerformed(ActionEvent e) {
   if (usageWindow != null) usageWindow.setVisible(true);
 }
 public void setUsageFileName(String fileName) {
   usageWindow = new HTMLViewFrame(fileName);
   usageWindow.setSize(450, 430);
 }