@Override
 public void focusLost(FocusEvent e) {
   if (field.getText().trim().equals("")) {
     field.setText(GUI.INPUT_NUMBER);
     field.setForeground(Color.GRAY);
   }
 }
 @Override
 public void focusGained(FocusEvent e) {
   if (field.getText().trim().equals(GUI.INPUT_NUMBER)) {
     field.setText("");
     field.setForeground(Color.BLACK);
   }
 }