Java 8 Date and Time API: Practical Examples and Usage

Java 8 introduced a new date‑time API (java.time) that is immutable and thread‑safe, addressing the shortcomings of java.util.Date and SimpleDateFormat.

Example 1: Get today’s date

package com.shxt.demo02;
import java.time.LocalDate;
public class Demo01 {
    public static void main(String[] args) {
        LocalDate today = LocalDate.now();
        System.out.println("今天的日期:" + today);
    }
}

Example 2: Get year, month, and day

package com.shxt.demo02;
import java.time.LocalDate;
public class Demo02 {
    public static void main(String[] args) {
        LocalDate today = LocalDate.now();
        int year = today.getYear();
        int month = today.getMonthValue();
        int day = today.getDayOfMonth();
        System.out.println("year:" + year);
        System.out.println("month:" + month);
        System.out.println("day:" + day);
    }
}

Example 3: Create a specific date

package com.shxt.demo02;
import java.time.LocalDate;
public class Demo03 {
    public static void main(String[] args) {
        LocalDate date = LocalDate.of(2018, 2, 6);
        System.out.println("自定义日期:" + date);
    }
}

Example 4: Compare two dates for equality

package com.shxt.demo02;
import java.time.LocalDate;
public class Demo04 {
    public static void main(String[] args) {
        LocalDate date1 = LocalDate.now();
        LocalDate date2 = LocalDate.of(2018, 2, 5);
        if (date1.equals(date2)) {
            System.out.println("时间相等");
        } else {
            System.out.println("时间不等");
        }
    }
}

Example 5: Check a recurring event such as a birthday

package com.shxt.demo02;
import java.time.LocalDate;
import java.time.MonthDay;
public class Demo05 {
    public static void main(String[] args) {
        LocalDate today = LocalDate.now();
        LocalDate birthdayDate = LocalDate.of(2018, 2, 6);
        MonthDay birthday = MonthDay.of(birthdayDate.getMonth(), birthdayDate.getDayOfMonth());
        MonthDay current = MonthDay.from(today);
        if (current.equals(birthday)) {
            System.out.println("是你的生日");
        } else {
            System.out.println("你的生日还没有到");
        }
    }
}

Example 6: Get the current time (without date)

package com.shxt.demo02;
import java.time.LocalTime;
public class Demo06 {
    public static void main(String[] args) {
        LocalTime time = LocalTime.now();
        System.out.println("获取当前的时间,不含有日期:" + time);
    }
}

Example 7: Add hours to the current time

package com.shxt.demo02;
import java.time.LocalTime;
public class Demo07 {
    public static void main(String[] args) {
        LocalTime time = LocalTime.now();
        LocalTime newTime = time.plusHours(3);
        System.out.println("三个小时后的时间为:" + newTime);
    }
}

Example 8: Calculate the date one week later

package com.shxt.demo02;
import java.time.LocalDate;
import java.time.temporal.ChronoUnit;
public class Demo08 {
    public static void main(String[] args) {
        LocalDate today = LocalDate.now();
        System.out.println("今天的日期为:" + today);
        LocalDate nextWeek = today.plus(1, ChronoUnit.WEEKS);
        System.out.println("一周后的日期为:" + nextWeek);
    }
}

Example 9: Calculate one year before and after today

package com.shxt.demo02;
import java.time.LocalDate;
import java.time.temporal.ChronoUnit;
public class Demo09 {
    public static void main(String[] args) {
        LocalDate today = LocalDate.now();
        LocalDate previousYear = today.minus(1, ChronoUnit.YEARS);
        System.out.println("一年前的日期 : " + previousYear);
        LocalDate nextYear = today.plus(1, ChronoUnit.YEARS);
        System.out.println("一年后的日期:" + nextYear);
    }
}

Example 10: Using the Clock class

package com.shxt.demo02;
import java.time.Clock;
public class Demo10 {
    public static void main(String[] args) {
        Clock clock = Clock.systemUTC();
        System.out.println("Clock : " + clock.millis());
        Clock defaultClock = Clock.systemDefaultZone();
        System.out.println("Clock : " + defaultClock.millis());
    }
}

Example 11: Determine if a date is before or after another date

package com.shxt.demo02;
import java.time.LocalDate;
import java.time.temporal.ChronoUnit;
public class Demo11 {
    public static void main(String[] args) {
        LocalDate today = LocalDate.now();
        LocalDate tomorrow = LocalDate.of(2018, 2, 6);
        if (tomorrow.isAfter(today)) {
            System.out.println("之后的日期:" + tomorrow);
        }
        LocalDate yesterday = today.minus(1, ChronoUnit.DAYS);
        if (yesterday.isBefore(today)) {
            System.out.println("之前的日期:" + yesterday);
        }
    }
}

Example 12: Working with time zones

package com.shxt.demo02;
import java.time.LocalDateTime;
import java.time.ZoneId;
import java.time.ZonedDateTime;
public class Demo12 {
    public static void main(String[] args) {
        ZoneId america = ZoneId.of("America/New_York");
        LocalDateTime localtDateAndTime = LocalDateTime.now();
        ZonedDateTime dateAndTimeInNewYork = ZonedDateTime.of(localtDateAndTime, america);
        System.out.println("Current date and time in a particular timezone : " + dateAndTimeInNewYork);
    }
}

Example 13: Representing fixed dates such as credit‑card expiry with YearMonth

package com.shxt.demo02;
import java.time.YearMonth;
import java.time.Month;
public class Demo13 {
    public static void main(String[] args) {
        YearMonth currentYearMonth = YearMonth.now();
        System.out.printf("Days in month year %s: %d%n", currentYearMonth, currentYearMonth.lengthOfMonth());
        YearMonth creditCardExpiry = YearMonth.of(2019, Month.FEBRUARY);
        System.out.printf("Your credit card expires on %s %n", creditCardExpiry);
    }
}

Example 14: Checking for a leap year

package com.shxt.demo02;
import java.time.LocalDate;
public class Demo14 {
    public static void main(String[] args) {
        LocalDate today = LocalDate.now();
        if (today.isLeapYear()) {
            System.out.println("This year is Leap year");
        } else {
            System.out.println("2018 is not a Leap year");
        }
    }
}

Example 15: Calculating months between two dates

package com.shxt.demo02;
import java.time.LocalDate;
import java.time.Period;
public class Demo15 {
    public static void main(String[] args) {
        LocalDate today = LocalDate.now();
        LocalDate java8Release = LocalDate.of(2018, 12, 14);
        Period periodToNextJavaRelease = Period.between(today, java8Release);
        System.out.println("Months left between today and Java 8 release : " + periodToNextJavaRelease.getMonths());
    }
}

Example 16: Getting the current timestamp with Instant

package com.shxt.demo02;
import java.time.Instant;
public class Demo16 {
    public static void main(String[] args) {
        Instant timestamp = Instant.now();
        System.out.println("What is value of this instant " + timestamp.toEpochMilli());
    }
}

Example 17: Parsing a date string with a predefined formatter

package com.shxt.demo02;
import java.time.LocalDate;
import java.time.format.DateTimeFormatter;
public class Demo17 {
    public static void main(String[] args) {
        String dayAfterTomorrow = "20180205";
        LocalDate formatted = LocalDate.parse(dayAfterTomorrow, DateTimeFormatter.BASIC_ISO_DATE);
        System.out.println(dayAfterTomorrow + "  格式化后的日期为:  " + formatted);
    }
}

Example 18: Converting between String and date types

package com.shxt.demo02;
import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
public class Demo18 {
    public static void main(String[] args) {
        LocalDateTime date = LocalDateTime.now();
        DateTimeFormatter format1 = DateTimeFormatter.ofPattern("yyyy/MM/dd HH:mm:ss");
        String str = date.format(format1);
        System.out.println("日期转换为字符串:" + str);
        DateTimeFormatter format2 = DateTimeFormatter.ofPattern("yyyy/MM/dd HH:mm:ss");
        LocalDate date2 = LocalDate.parse(str, format2);
        System.out.println("日期类型:" + date2);
    }
}