java 获得某月的第一天和最后一天

/** * 得到本月的第一天   * @return   */  public static String getMonthFirstDay() {   SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");    Calendar calendar = Calendar.getInstance();       calendar.set(Calendar.DAY_OF_MONTH, calendar               .getActualMinimum(Calendar.DAY_OF_MONTH));         return sdf.format(calendar.getTime());   }     /**   * 得到本月的最后一天   *    * @return   */  public static String getMonthLastDay() {   SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");    Calendar calendar = Calendar.getInstance();       calendar.set(Calendar.DAY_OF_MONTH, calendar               .getActualMaximum(Calendar.DAY_OF_MONTH));       return sdf.format(calendar.getTime());  }