JDK8之前
日期與時間戳之間的轉換
public class Test {
public static void main(String[] args) {
Date date = new Date();
System.out.println("date = " + date); // date = Sun Sep 26 14:48:52 CST 2021
Date date1 = new Date(1632638970000L);
System.out.println("date1 = " + date1); // date1 = Sun Sep 26 14:49:30 CST 2021
long time = date.getTime();
System.out.println("time = " + time); // time = 1632639026166
date.setTime(1632638970000L);
System.out.println("date = " + date); // date = Sun Sep 26 14:49:30 CST 2021
}
}
日曆獲取年月日欄位
public class Test {
public static void main(String[] args) {
Calendar calendar = Calendar.getInstance();
int year = calendar.get(Calendar.YEAR);
int month = calendar.get(Calendar.MONTH) + 1;
int day = calendar.get(Calendar.DAY_OF_MONTH);
int hour = calendar.get(Calendar.HOUR_OF_DAY);
int minute = calendar.get(Calendar.MINUTE);
int second = calendar.get(Calendar.SECOND);
int milliSecond = calendar.get(Calendar.MILLISECOND);
// 2021-9-26 15:14:6:16
System.out.print(year + "-" + month + "-" + day + " " + hour + ":" + minute + ":" + second + ":" + milliSecond);
}
}
日期格式化
public class Test {
public static void main(String[] args) throws ParseException {
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
Date date = new Date();
// 將日期物件格式化為字串
String format = sdf.format(date);
System.out.println("format = " + format); // format = 2021-09-26 16:02:17
// 將字串解析為日期物件
Date parse = sdf.parse(format);
System.out.println("parse = " + parse); // parse = Sun Sep 26 16:02:17 CST 2021
}
}
JDK8之後
之前存在的問題
- Java 1.0 中包含了一個 Date 類,但是它的大多數方法已經在 Java 1.1 中引入 Calendar 類的時候被廢棄了。
-
格式化只對 Date 有效,Calendar 則不行。
-
它們不是執行緒安全的,不能處理閏秒等
注:API 功能更加強大,但好像用的更多的還是老版本寫法
本地日期時間
-
Instant 是帶時區的(以UTC為準),用來替換以前的 Date
-
LocalDateTIme 是不帶時區(以本地時區為準)的,用來替換以前的 Calendar
public class Test {
public static void main(String[] args) {
LocalDate now = LocalDate.now();
System.out.println("now = " + now); // now = 2021-09-26
LocalTime now1 = LocalTime.now();
System.out.println("now1 = " + now1); // now1 = 20:02:32.659
LocalDateTime now2 = LocalDateTime.now();
System.out.println("now2 = " + now2); // now2 = 2021-09-26T20:02:32.660
Instant now = Instant.now();
System.out.println("now = " + now); // now = 2021-09-27T01:54:39.351Z
LocalDateTime now1 = LocalDateTime.now();
System.out.println("now1 = " + now1); // now1 = 2021-09-27T09:54:39.401
LocalDateTime now = LocalDateTime.now();
int year = now.getYear();
System.out.println("獲取年份:" + year);
int monthValue = now.getMonthValue();
System.out.println("獲取月份:" + monthValue);
int dayOfMonth = now.getDayOfMonth();
System.out.println("獲取天數:" + dayOfMonth);
int dayOfYear = now.getDayOfYear();
System.out.println("獲取一年中的第" + dayOfYear + "天");
DayOfWeek dayOfWeek = now.getDayOfWeek();
System.out.println("獲取星期" + dayOfWeek.getValue());
int hour = now.getHour();
System.out.println("獲取小時:" + hour);
int minute = now.getMinute();
System.out.println("獲取分鐘:" + minute);
int second = now.getSecond();
System.out.println("獲取秒:" + second);
int nano = now.getNano();
System.out.println("獲取納秒:" + nano);
}
}
日期格式化
public class Test {
public static void main(String[] args) {
DateTimeFormatter df = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
// 將日期格式化為字串
String format = df.format(LocalDateTime.now());
System.out.println("format = " + format); // format = 2021-09-27 13:55:51
// 將字串解析為日期
TemporalAccessor parse = df.parse("2011-11-11 11:11:11");
LocalDateTime from = LocalDateTime.from(parse);
System.out.println("from = " + from); // from = 2011-11-11T11:11:11
}
}