Java 8 Add Days to Current Date Example

1. Introduction

Java 8 added a new set of packages to provide a comprehensive date-time model. Java 8 Date-Time API is a JSR-310 implementation. In this example, I will use classes from the java.time and java.time.format packages to demonstrate how to add days to the current date.

• java.time is the base package which includes a set of date-time classes: LocalDate, LocalDateTime, Instant, Period, Duration, Clock, ZonedDateTime, etc. These classes use the calendar system defined in ISO-8601 as the default calendar. Each class has a now() method to get the current date and common utility operations: plus, minus, format, etc.
• java.time.format includes classes for formatting and parsing date and time objects.

2. Technologies used

The example code in this article was built and run using:

• Java 1.8.101
• Maven 3.3.9
• Eclipse Oxygen
• JUnit 4.12

3. Maven Project

3.1 Dependency

Add Junit to the pom.xml.

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<groupId>zheng.jcg.demo</groupId>
	<artifactId>java8-date</artifactId>
	<version>0.0.1-SNAPSHOT</version>

	<dependencies>
		<dependency>
			<groupId>junit</groupId>
			<artifactId>junit</artifactId>
			<version>4.12</version>
			<scope>test</scope>
		</dependency>
	</dependencies>
	<build>
		<plugins>
			<plugin>
				<artifactId>maven-compiler-plugin</artifactId>
				<version>3.3</version>
				<configuration>
					<source>1.8</source>
					<target>1.8</target>
				</configuration>
			</plugin>
		</plugins>
	</build>
</project>

3.2 Add Days with LocalDate

LocalDate is a date class without a time-zone in the ISO-8601 calendar system, such as 2018-10-25.

In this step, I will demonstrate how to add days to the current date using LocalDate in two steps:

1. Get the current date via the now method.
2. Add days via the plusDays and plus methods.

AddDays_LocalDate.java

package com.zheng.demo;

import java.time.LocalDate;
import java.time.Period;
import java.time.ZoneId;
import java.time.temporal.ChronoUnit;

public class AddDays_LocalDate {
	private LocalDate currentDate;

	public AddDays_LocalDate() {
		super();
		currentDate = LocalDate.now();
	}
	
	public AddDays_LocalDate(ZoneId zoneId) {
		currentDate = LocalDate.now(zoneId);
	}

	public LocalDate addDays_by_plusDays(Long days) {
		return currentDate.plusDays(days.longValue());
	}
	
	public LocalDate addDays_by_plus(Long days) {
		return currentDate.plus(Period.ofDays(days.intValue()));
	}
	
	public LocalDate addDays_by_plus_2(Long days) {
		return currentDate.plus(days.longValue(), ChronoUnit.DAYS);
	}

	public LocalDate substractDays_by_minusDays(Long days) {
		return currentDate.minusDays(days.longValue());
	}

	public LocalDate getCurrentDate() {
		return currentDate;
	}

	public void setCurrentDate(LocalDate currentDate) {
		this.currentDate = currentDate;
	}

}

3.3 Add Days with LocalDateTime

LocalDateTime is a date-time class without a time-zone in the ISO-8601 calendar system, such as 2018-10-25T10:15:30.

In this step, I will demonstrate how to add days to the current date using LocalDateTime via plus and plusDays.

AddDays_LocalDateTime.java

package com.zheng.demo;

import java.time.LocalDateTime;
import java.time.Period;
import java.time.ZoneId;
import java.time.temporal.ChronoUnit;

public class AddDays_LocalDateTime {
	private LocalDateTime currentDate;

	public AddDays_LocalDateTime() {
		super();
		currentDate = LocalDateTime.now();
	}
	
	public AddDays_LocalDateTime(ZoneId zoneId) {
		currentDate = LocalDateTime.now(zoneId);
	}

	public LocalDateTime addDays_by_plusDays(Long days) {
		return currentDate.plusDays(days.longValue());
	}
	
	public LocalDateTime addDays_by_plus(Long days) {
		return currentDate.plus(Period.ofDays( days.intValue()));
	}
	
	public LocalDateTime addDays_by_plus_2(Long days) {
		return currentDate.plus(days.longValue(), ChronoUnit.DAYS);
	}

	public LocalDateTime substractDays_by_minusDays(Long days) {
		return currentDate.minusDays(days.longValue());
	}

	public LocalDateTime getCurrentDate() {
		return currentDate;
	}

	public void setCurrentDate(LocalDateTime currentDate) {
		this.currentDate = currentDate;
	}

}

3.4 Add Days with ZonedDateTime

ZonedDateTime is a date-time class with a time-zone in the ISO-8601 calendar system, such as 2018-10-25T10:15:30+01:00 US/Central.

In this step, I will demonstrate how to add days to the current date using ZonedDateTime via plus and plusDays.

AddDays_ZonedDateTime.java

package com.zheng.demo;

import java.time.Period;
import java.time.ZonedDateTime;
import java.time.temporal.ChronoUnit;

public class AddDays_ZonedDateTime {
	private ZonedDateTime currentDate;

	public AddDays_ZonedDateTime() {
		super();
		currentDate = ZonedDateTime.now();
	}

	public ZonedDateTime addDays_by_plusDays(Long days) {
		return currentDate.plusDays(days.longValue());
	}
	
	public ZonedDateTime addDays_by_plus(Long days) {
		return currentDate.plus(Period.ofDays(days.intValue()));
	}
	
	public ZonedDateTime addDays_by_plus_2(Long days) {
		return currentDate.plus(days.longValue(), ChronoUnit.DAYS);
	}
	
	public ZonedDateTime substractDays_by_minusDays(Long days) {
		return currentDate.minusDays(days.longValue());
	}

	public ZonedDateTime getCurrentDate() {
		return currentDate;
	}

	public void setCurrentDate(ZonedDateTime currentDate) {
		this.currentDate = currentDate;
	}

}

3.5 Add Days with Instant

Instant models a single instantaneous point on the timeline.

In this step, I will demonstrate how to add days to the current date using Instant via plus.

AddDays_Instant.java

package com.zheng.demo;

import java.time.Duration;
import java.time.Instant;
import java.time.temporal.ChronoUnit;

public class AddDays_Instant {
	private Instant currentDate;

	public AddDays_Instant() {
		super();
		currentDate = Instant.now();
	}

	public Instant addDays_by_plus_2(Long days) {
		return currentDate.plus(days.longValue(), ChronoUnit.DAYS);
	}
	
	public Instant addDays_by_plus(Long days) {
		return currentDate.plus(Duration.ofDays(days.longValue()));
	}

	public Instant substractDaysWithMinus(Long days) {
		return currentDate.minus(days.longValue(), ChronoUnit.DAYS);
	}

	public Instant getCurrentDate() {
		return currentDate;
	}

	public void setCurrentDate(Instant currentDate) {
		this.currentDate = currentDate;
	}

}

3.6 Add Days with Clock

Clock provides access to the current instant, date, and time.

In this step, I will demonstrate how to add days to the current date using Clock via instant.

AddDays_Clock.java

package com.zheng.demo;

import java.time.Clock;
import java.time.Instant;
import java.time.temporal.ChronoUnit;

public class AddDays_Clock {
	private Instant currentDate;

	public AddDays_Clock() {
		super();
		currentDate = Clock.systemUTC().instant();
	}

	public Instant addDays(Long days) {
		return currentDate.plus(days.longValue(), ChronoUnit.DAYS);
	}

	public Instant substractDays(Long days) {
		return currentDate.minus(days.longValue(), ChronoUnit.DAYS);
	}

	public Instant getCurrentDate() {
		return currentDate;
	}

	public void setCurrentDate(Instant currentDate) {
		this.currentDate = currentDate;
	}

}

4. JUnit Tests

4.1 AddDays_LocalDateTest

I will use the Java 8 DateTimeFormatter to format the LocalDate as "yyyy/MM/dd" and test it by adding days to the current date.

AddDays_LocalDateTest.java

package com.zheng.demo;

import static org.junit.Assert.assertTrue;

import java.time.LocalDate;
import java.time.ZoneId;
import java.time.format.DateTimeFormatter;

import org.junit.Before;
import org.junit.Test;

public class AddDays_LocalDateTest {

	private static final int DAYS = 10;
	private static final String ISO8601_DATE_FORMAT = "yyyy/MM/dd";
	private static final DateTimeFormatter dateFormat8 = DateTimeFormatter.ofPattern(ISO8601_DATE_FORMAT);

	private AddDays_LocalDate defaultZoneDate = new AddDays_LocalDate();
	private AddDays_LocalDate cstZoneDate = new AddDays_LocalDate(ZoneId.of("US/Central"));

	@Before
	public void setup() {
		System.out.println("*****\nOriginal defaultZoneDate : " + dateFormat8.format(defaultZoneDate.getCurrentDate()));
		System.out.println("*****\nOriginal cstZoneDate : " + dateFormat8.format(cstZoneDate.getCurrentDate()));
		System.out.println("-----");
	}

	@Test
	public void test_addDays_by_plusDays() {
		for (int i = 0; i < DAYS; i++) {
			LocalDate plusDate = defaultZoneDate.addDays_by_plusDays(Long.valueOf(i));
			assertTrue( i == plusDate.getDayOfYear() - defaultZoneDate.getCurrentDate().getDayOfYear());
			
			System.out.println(" Plus " + i + " days = " + dateFormat8.format(plusDate));
		}
	}

	@Test
	public void test_substractDays_by_minusDays() {
		for (int i = 0; i < DAYS; i++) {
			LocalDate minusDate = defaultZoneDate.substractDays_by_minusDays(Long.valueOf(i));
			assertTrue( i ==  defaultZoneDate.getCurrentDate().getDayOfYear() - minusDate.getDayOfYear());
			
			System.out.println(" Minus " + i + " days = " + dateFormat8.format(minusDate));
		}
	}

}

4.2 AddDays_LocalDateTimeTest

I will use the Java 8 DateTimeFormatter to format the LocalDateTime as "yyyy/MM/dd HH:mm:ss" and test it by adding days to the current date.

AddDays_LocalDateTimeTest.java

package com.zheng.demo;

import static org.junit.Assert.assertTrue;

import java.time.LocalDateTime;
import java.time.ZoneId;
import java.time.format.DateTimeFormatter;

import org.junit.Before;
import org.junit.Test;

public class AddDays_LocalDateTimeTest {

	private static final int DAYS = 10;
	private static final String ISO8601_DATE_FORMAT = "yyyy/MM/dd HH:mm:ss";
	private static final DateTimeFormatter dateFormat8 = DateTimeFormatter.ofPattern(ISO8601_DATE_FORMAT);

	private AddDays_LocalDateTime defaultZoneDate = new AddDays_LocalDateTime();
	private AddDays_LocalDateTime cstZoneDate = new AddDays_LocalDateTime(ZoneId.of("US/Central"));

	@Before
	public void setup() {
		System.out.println("*****\nOriginal defaultZoneDate : " + dateFormat8.format(defaultZoneDate.getCurrentDate()));
		System.out.println("*****\nOriginal cstZoneDate : " + dateFormat8.format(cstZoneDate.getCurrentDate()));
		System.out.println("-----");
	}

	@Test
	public void plus_number_of_days() {
		for (int i = 0; i < DAYS; i++) {
			LocalDateTime plusDate = defaultZoneDate.addDays_by_plusDays(Long.valueOf(i));			
			assertTrue( i == plusDate.getDayOfYear() - defaultZoneDate.getCurrentDate().getDayOfYear());
			System.out.println("Plus " + i + " = " + dateFormat8.format(plusDate));
		}
	}

	@Test
	public void minus_number_of_days() {
		for (int i = 0; i < DAYS; i++) {
			LocalDateTime minusDate = defaultZoneDate.substractDays_by_minusDays(Long.valueOf(i));
			assertTrue( i ==  defaultZoneDate.getCurrentDate().getDayOfYear() - minusDate.getDayOfYear());
			
			System.out.println("Minus" + i + " = " + dateFormat8.format(minusDate));
		}
	}

}

4.3 AddDays_ZondedDateTimeTest

I will use the Java 8 ZonedTimeFormatter to format the ZondedDateTime and test it by adding days to the current date.

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AddDays_ZondedDateTimeTest.java

package com.zheng.demo;

import static org.junit.Assert.assertTrue;

import java.time.ZonedDateTime;
import java.time.format.DateTimeFormatter;

import org.junit.Before;
import org.junit.Test;

public class AddDays_ZonedDateTimeTest {

	private static final int DAYS = 10;

	private static final DateTimeFormatter dateFormat8 = DateTimeFormatter.ISO_OFFSET_DATE_TIME;

	private AddDays_ZonedDateTime defaultZoneDate = new AddDays_ZonedDateTime();

	@Before
	public void setup() {
		System.out.println("*****\nOriginal defaultZoneDate : " + dateFormat8.format(defaultZoneDate.getCurrentDate()));
		System.out.println("-----");
	}

	@Test
	public void add_number_of_days_byPlusDays() {
		for (int i = 1; i < DAYS; i++) {
			ZonedDateTime plusDate = defaultZoneDate.addDays_by_plusDays(Long.valueOf(i));
			assertTrue( i == plusDate.getDayOfYear() - defaultZoneDate.getCurrentDate().getDayOfYear());
			
			System.out.println("PlusDays " + i + " = " + dateFormat8.format(plusDate));
		}
	}

	@Test
	public void add_number_of_days_byPlus() {
		for (int i = 1; i < DAYS; i++) {
			ZonedDateTime plusDate = defaultZoneDate.addDays_by_plus(Long.valueOf(i));
			assertTrue( i == plusDate.getDayOfYear() - defaultZoneDate.getCurrentDate().getDayOfYear());
			
			System.out.println("Plus " + i + "= " + dateFormat8.format(plusDate));
		}
	}

}

4.4 AddDays_InstantTest

I will add days to the current date with Instant.

AddDays_InstantTest.java

package com.zheng.demo;

import java.time.Instant;

import org.junit.Before;
import org.junit.Test;

public class AddDays_InstantTest {

	private AddDays_Instant defaultZoneDate = new AddDays_Instant();

	@Before
	public void setup() {
		System.out.println("*****\nOriginal defaultZoneDate : " + defaultZoneDate.getCurrentDate());
		System.out.println("-----");
	}

	@Test
	public void plus_number_of_days() {
		for (int i = 0; i < 10; i++) {
			Instant plusDate = defaultZoneDate.addDays_by_plus(Long.valueOf(i));
			System.out.println("Plus " + i + " = " + plusDate);
		}
	}

	@Test
	public void minus_number_of_days() {
		for (int i = 0; i < 10; i++) {
			Instant minusDate = defaultZoneDate.substractDaysWithMinus(Long.valueOf(i));
			System.out.println("Minus" + i + "= " + minusDate);
		}
	}

}

4.5 AddDays_ClockTest

I will add days to the current date with the Clock.

AddDays_ClockTest.java

package com.zheng.demo;

import java.time.Instant;

import org.junit.Before;
import org.junit.Test;

public class AddDays_ClockTest {

	private AddDays_Clock defaultZoneDate = new AddDays_Clock();

	@Before
	public void setup() {
		System.out.println("*****\nOriginal defaultZoneDate : " + defaultZoneDate.getCurrentDate());
		System.out.println("-----");
	}

	@Test
	public void plus_number_of_days() {
		for (int i = 1; i < 10; i++) {
			Instant plusDate = defaultZoneDate.addDays(Long.valueOf(i));
			System.out.println("defaultZoneDate Plus " + i + " = " + plusDate);
		}
	}

	@Test
	public void minus_number_of_days() {
		for (int i = 1; i < 10; i++) {
			Instant minusDate = defaultZoneDate.substractDays(Long.valueOf(i));
			System.out.println("defaultZoneDate Minus" + i + "= " + minusDate);
		}
	}

}

5. Demo

Execute mvn clean install and capture the output:

Tests Output

--------------
 T E S T S
-------------------------------------------------------
Running com.zheng.demo.AddDays_ClockTest
*****
Original defaultZoneDate : 2018-10-25T19:30:20.773Z
-----
defaultZoneDate Minus1= 2018-10-24T19:30:20.773Z
defaultZoneDate Minus2= 2018-10-23T19:30:20.773Z
defaultZoneDate Minus3= 2018-10-22T19:30:20.773Z
defaultZoneDate Minus4= 2018-10-21T19:30:20.773Z
defaultZoneDate Minus5= 2018-10-20T19:30:20.773Z
defaultZoneDate Minus6= 2018-10-19T19:30:20.773Z
defaultZoneDate Minus7= 2018-10-18T19:30:20.773Z
defaultZoneDate Minus8= 2018-10-17T19:30:20.773Z
defaultZoneDate Minus9= 2018-10-16T19:30:20.773Z
*****
Original defaultZoneDate : 2018-10-25T19:30:20.824Z
-----
defaultZoneDate Plus 1 = 2018-10-26T19:30:20.824Z
defaultZoneDate Plus 2 = 2018-10-27T19:30:20.824Z
defaultZoneDate Plus 3 = 2018-10-28T19:30:20.824Z
defaultZoneDate Plus 4 = 2018-10-29T19:30:20.824Z
defaultZoneDate Plus 5 = 2018-10-30T19:30:20.824Z
defaultZoneDate Plus 6 = 2018-10-31T19:30:20.824Z
defaultZoneDate Plus 7 = 2018-11-01T19:30:20.824Z
defaultZoneDate Plus 8 = 2018-11-02T19:30:20.824Z
defaultZoneDate Plus 9 = 2018-11-03T19:30:20.824Z
Tests run: 2, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.154 sec
Running com.zheng.demo.AddDays_InstantTest
*****
Original defaultZoneDate : 2018-10-25T19:30:20.829Z
-----
Minus0= 2018-10-25T19:30:20.829Z
Minus1= 2018-10-24T19:30:20.829Z
Minus2= 2018-10-23T19:30:20.829Z
Minus3= 2018-10-22T19:30:20.829Z
Minus4= 2018-10-21T19:30:20.829Z
Minus5= 2018-10-20T19:30:20.829Z
Minus6= 2018-10-19T19:30:20.829Z
Minus7= 2018-10-18T19:30:20.829Z
Minus8= 2018-10-17T19:30:20.829Z
Minus9= 2018-10-16T19:30:20.829Z
*****
Original defaultZoneDate : 2018-10-25T19:30:20.831Z
-----
Plus 0 = 2018-10-25T19:30:20.831Z
Plus 1 = 2018-10-26T19:30:20.831Z
Plus 2 = 2018-10-27T19:30:20.831Z
Plus 3 = 2018-10-28T19:30:20.831Z
Plus 4 = 2018-10-29T19:30:20.831Z
Plus 5 = 2018-10-30T19:30:20.831Z
Plus 6 = 2018-10-31T19:30:20.831Z
Plus 7 = 2018-11-01T19:30:20.831Z
Plus 8 = 2018-11-02T19:30:20.831Z
Plus 9 = 2018-11-03T19:30:20.831Z
Tests run: 2, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.014 sec
Running com.zheng.demo.AddDays_LocalDateTest
*****
Original defaultZoneDate : 2018/10/25
*****
Original cstZoneDate : 2018/10/25
-----
 Plus 0 days = 2018/10/25
 Plus 1 days = 2018/10/26
 Plus 2 days = 2018/10/27
 Plus 3 days = 2018/10/28
 Plus 4 days = 2018/10/29
 Plus 5 days = 2018/10/30
 Plus 6 days = 2018/10/31
 Plus 7 days = 2018/11/01
 Plus 8 days = 2018/11/02
 Plus 9 days = 2018/11/03
*****
Original defaultZoneDate : 2018/10/25
*****
Original cstZoneDate : 2018/10/25
-----
 Minus 0 days = 2018/10/25
 Minus 1 days = 2018/10/24
 Minus 2 days = 2018/10/23
 Minus 3 days = 2018/10/22
 Minus 4 days = 2018/10/21
 Minus 5 days = 2018/10/20
 Minus 6 days = 2018/10/19
 Minus 7 days = 2018/10/18
 Minus 8 days = 2018/10/17
 Minus 9 days = 2018/10/16
Tests run: 2, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.048 sec
Running com.zheng.demo.AddDays_LocalDateTimeTest
*****
Original defaultZoneDate : 2018/10/25 14:30:20
*****
Original cstZoneDate : 2018/10/25 14:30:20
-----
Minus0 = 2018/10/25 14:30:20
Minus1 = 2018/10/24 14:30:20
Minus2 = 2018/10/23 14:30:20
Minus3 = 2018/10/22 14:30:20
Minus4 = 2018/10/21 14:30:20
Minus5 = 2018/10/20 14:30:20
Minus6 = 2018/10/19 14:30:20
Minus7 = 2018/10/18 14:30:20
Minus8 = 2018/10/17 14:30:20
Minus9 = 2018/10/16 14:30:20
*****
Original defaultZoneDate : 2018/10/25 14:30:20
*****
Original cstZoneDate : 2018/10/25 14:30:20
-----
Plus 0 = 2018/10/25 14:30:20
Plus 1 = 2018/10/26 14:30:20
Plus 2 = 2018/10/27 14:30:20
Plus 3 = 2018/10/28 14:30:20
Plus 4 = 2018/10/29 14:30:20
Plus 5 = 2018/10/30 14:30:20
Plus 6 = 2018/10/31 14:30:20
Plus 7 = 2018/11/01 14:30:20
Plus 8 = 2018/11/02 14:30:20
Plus 9 = 2018/11/03 14:30:20
Tests run: 2, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.065 sec
Running com.zheng.demo.AddDays_ZonedDateTimeTest
*****
Original defaultZoneDate : 2018-10-25T14:30:20.876-05:00
-----
PlusDays 1 = 2018-10-26T14:30:20.876-05:00
PlusDays 2 = 2018-10-27T14:30:20.876-05:00
PlusDays 3 = 2018-10-28T14:30:20.876-05:00
PlusDays 4 = 2018-10-29T14:30:20.876-05:00
PlusDays 5 = 2018-10-30T14:30:20.876-05:00
PlusDays 6 = 2018-10-31T14:30:20.876-05:00
PlusDays 7 = 2018-11-01T14:30:20.876-05:00
PlusDays 8 = 2018-11-02T14:30:20.876-05:00
PlusDays 9 = 2018-11-03T14:30:20.876-05:00
*****
Original defaultZoneDate : 2018-10-25T14:30:20.882-05:00
-----
Plus 1= 2018-10-26T14:30:20.882-05:00
Plus 2= 2018-10-27T14:30:20.882-05:00
Plus 3= 2018-10-28T14:30:20.882-05:00
Plus 4= 2018-10-29T14:30:20.882-05:00
Plus 5= 2018-10-30T14:30:20.882-05:00
Plus 6= 2018-10-31T14:30:20.882-05:00
Plus 7= 2018-11-01T14:30:20.882-05:00
Plus 8= 2018-11-02T14:30:20.882-05:00
Plus 9= 2018-11-03T14:30:20.882-05:00
Tests run: 2, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.08 sec

Results :

Tests run: 10, Failures: 0, Errors: 0, Skipped: 0

6. Java 8 Add Days to Current Date Example- Summary

In this example, we demonstrated how to add days to the current date via the classes: LocalDate, LocalDateTime, ZonedDateTime, Instant, and Clock.

7. Download the Source Code

This example consists of a Maven project to add days to the current date using Java 8 Date-Time API.

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