//1、使用 Date 对象并格式化

Date date1 = new Date();

DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

String dateStr = dateFormat.format(date1);

System.out.println(dateStr);

//2、使用 Calendar 对象

Calendar calendar = Calendar.getInstance();

System.out.println(calendar.getTime().toLocaleString());

//3、使用 DateFormat 对象

DateFormat dateTimeInstance = DateFormat.getDateTimeInstance();

String format = dateTimeInstance.format(new Date());

System.out.println(format);

// 使用 Calendar 对象

Calendar calendar = Calendar.getInstance();

// 日期格式化对象

DateFormat dateformat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

//1、获取当前时间

calendar.setTime(calendar.getTime());

Date nowDate = calendar.getTime();

String nowDateStr = dateformat.format(nowDate);

System.out.println(nowDateStr);

//2、当前时间增加 24 小时

calendar.add(Calendar.HOUR, 24);

Date addition24HourDate = calendar.getTime();

String addition24DateStr = dateformat.format(addition24HourDate);

System.out.println(addition24DateStr);

//3、再增加 5 分钟

calendar.add(Calendar.MINUTE, 5);

Date addition5MinuteDate = calendar.getTime();

String addition5MinuteDateStr = dateformat.format(addition5MinuteDate);

System.out.println(addition5MinuteDateStr);

//4、再增加 1 年

calendar.add(Calendar.YEAR, 1);

Date addition1YearDate = calendar.getTime();

String addition1YearDateStr = dateformat.format(addition1YearDate);

System.out.println(addition1YearDateStr);

// 使用 Date 对象

//1、指定两个 Date 对象

DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

Date nowDate = new Date();

String yesterday = "2023-09-01 10:00:00";

Date yesterdayDate = dateFormat.parse(yesterday);

//2、时间戳相减（毫秒）

long yesterdayDateTime = yesterdayDate.getTime();

long nowDateTime = nowDate.getTime();

int result = (int) (nowDateTime - yesterdayDateTime);

//3、换算成秒

int diffSecond = result / 1000;

System.out.println(diffSecond);

//4、换算成分钟

int diffMinute = result / 1000 / 60;

System.out.println(diffMinute);

//5、换算成小时

int diffHour = result / 1000 / 60 / 60;

System.out.println(diffHour);

//6、换算成天

int diffDay = result / 86400000;

System.out.println(diffDay);