JAVA 中消息提示框的写法！

JOptionPane.showMessageDialog(null,"弹出的是消息提示框!", "系统信息", JOptionPane.INFORMATION_MESSAGE);
JOptionPane.showMessageDialog(null,"弹出的是警告提示框!", "系统信息", JOptionPane.WARNING_MESSAGE);
JOptionPane.showMessageDialog(null,"弹出的是错误提示框!", "系统信息", JOptionPane.ERROR_MESSAGE);
JOptionPane.showMessageDialog(null,"弹出的是询问提示框!", "系统信息", JOptionPane.QUESTION_MESSAGE);

int option = JOptionPane.showConfirmDialog(null,
       "文件已修改，是否保存？", "保存文件？", JOptionPane.YES_NO_OPTION,
       JOptionPane.WARNING_MESSAGE, null);
     switch (option) {
     case JOptionPane.YES_NO_OPTION: {
      saveAsFile();
      break;
     }
     case JOptionPane.NO_OPTION:
      System.exit(0);

     }