Calendar calendar = Calendar.getInstance();

// 获取当前年

int year = calendar.get(Calendar.YEAR);

// 获取当前月

int month = calendar.get(Calendar.MONTH) + 1;

// 获取当前日

int day = calenedar.get(Calendar.DATE);

// 获取当前小时

int hour = calendar.get(Calendar.HOUR_OF_DAY);

// 获取当前分钟

int minute = calendar.get(Calendar.MINUTE);

// 获取当前秒

int second = calendar.get(Calendar.SECOND);

// 获取当前是本周第几天

int dayOfWeek = calendar.get(Calendar.DAY_OF_WEEK);

// 获取当前是本月第几天

int dayOfMonth = calendar.get(Calendar.DAY_OF_MONTH);

// 获取当前是本年第几天

int dayOfYear = calendar.get(Calendar.DAY_OF_YEAR);

SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");

// 获取当月第一天

calendar = Calendar.getInstance();

calendar.add(Calendar.MONTH, 0);

calendar.set(Calendar.DAY_OF_MONTH, 1);

String firstday = format.format(calendar.getTime());

// 获取当月最后一天

calendar = Calendar.getInstance();

calendar.add(Calendar.MONTH, 1);

calendar.set(Calendar.DAY_OF_MONTH, 0);

String lastday = format.format(calendar.getTime());

// 打印结果字符串

System.out.println("本月第一天和最后一天分别是：" + firstday + " 和 " + lastday + "。");

SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");

Date date = new Date();

System.out.println("当前日期字符串：" + format.format(date) + "。");