Table of Contents

LocalDate in Java with Examples

是一個不可變的類別，表示日期，預設格式為 yyyy-mm-dd，建立日期的方式重新被定義，使用上更加簡便，LocalDate in Java 介紹常見的 format 、 parse 、 ofEpochDay 等方法，本篇增加了範例，並透過單元測試來驗證產出結果。

檔案目錄

./
   +- src
       +- test
       |   +- org
       |       +- ruoxue
       |           +- java_147
       |               +- datetime
       |                   +- localdate
       |                       +- LocalDateWithExamplesTest.java

單元測試

提供日期建立、格式化等操作 LocalDate 。

format

建立一個 LocalDate ，格式化指定日期。

	@Test
	public void format() {
		LocalDate localDate = LocalDate.of(2023, 6, 18);
		String result = localDate.format(DateTimeFormatter.ISO_LOCAL_DATE);
		System.out.println(result);
		assertEquals("2023-06-18", result);
		
		result = localDate.format(DateTimeFormatter.ofPattern("yyyyMMdd"));
		System.out.println(result);
		assertEquals("20230618", result);

		result = localDate.format(DateTimeFormatter.ofPattern("yyyy/MM/dd"));
		System.out.println(result);
		assertEquals("2023/06/18", result);
	}

2023-06-18
20230618
2023/06/18

parse

LocalDate Java 建立一個 LocalDate ，使用 String 建立指定日期。

	@Test
	public void parse() {
		LocalDate localDate = LocalDate.parse("2023-06-18");
		System.out.println(localDate);
		assertEquals("2023-06-18", localDate.toString());

		localDate = LocalDate.parse("20230618", DateTimeFormatter.ofPattern("yyyyMMdd"));
		System.out.println(localDate);
		assertEquals("2023-06-18", localDate.toString());

		localDate = LocalDate.parse("2023/06/18", DateTimeFormatter.ofPattern("yyyy/MM/dd"));
		System.out.println(localDate);
		assertEquals("2023-06-18", localDate.toString());
	}

2023-06-18
2023-06-18
2023-06-18

from

建立一個 LocalDate ，從另一個日期，建立指定日期。

	@Test
	public void from() {
		LocalDate localDate = LocalDate.parse("2023-06-18");
		LocalDate result = LocalDate.from(localDate);
		System.out.println(result);
		assertEquals("2023-06-18", result.toString());

		LocalDateTime localDateTime = LocalDateTime.parse("2023-06-18T09:12:05");
		ZoneOffset zoneOffset = ZoneOffset.of("+05:00");
		OffsetDateTime offsetDateTime = OffsetDateTime.of(localDateTime, zoneOffset);
		System.out.println(offsetDateTime);
		result = LocalDate.from(offsetDateTime);
		System.out.println(result);
		assertEquals("2023-06-18", result.toString());

		ZonedDateTime zonedDateTime = ZonedDateTime.parse("2023-06-18T09:12:05+05:00[America/Chicago]");
		result = LocalDate.from(zonedDateTime);
		System.out.println(result);
		assertEquals("2023-06-18", result.toString());
	}

2023-06-18
2023-06-18T09:12:05+05:00
2023-06-18
2023-06-18

toEpochDay

Java LocalDate 建立一個 LocalDate ，取得紀元日，從 UTC 的 1970-01-01T00:00:00Z 起。

	@Test
	public void toEpochDay() {
		LocalDate localDate = LocalDate.of(2023, 6, 18);
		long result = localDate.toEpochDay();
		System.out.println(result);
		assertEquals(19526L, result);
	}

ofEpochDay

建立一個 LocalDate ，將紀元日轉成指定日期。

	@Test
	public void ofEpochDay() {
		LocalDate localDate = LocalDate.ofEpochDay(19526L);
		System.out.println(localDate);
		assertEquals("2023-06-18", localDate.toString());
	}

2023-06-18

ofYearDay

建立一個 LocalDate ，將本年日轉成指定日期。

	@Test
	public void ofYearDay() {
		LocalDate localDate = LocalDate.ofYearDay(2023, 169);
		System.out.println(localDate);
		assertEquals("2023-06-18", localDate.toString());
	}

2023-06-18

LocalDateWithExamplesTest.java

LocalDate in Java 新增單元測試，驗證 Java LocalDate Example 是否符合預期。

package org.ruoxue.java_147.datetime.localdate;

import static org.junit.Assert.*;

import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.OffsetDateTime;
import java.time.ZoneOffset;
import java.time.ZonedDateTime;
import java.time.format.DateTimeFormatter;

import org.junit.Test;

public class LocalDateWithExamplesTest {

	@Test
	public void format() {
		LocalDate localDate = LocalDate.of(2023, 6, 18);
		String result = localDate.format(DateTimeFormatter.ISO_LOCAL_DATE);
		System.out.println(result);
		assertEquals("2023-06-18", result);
		
		result = localDate.format(DateTimeFormatter.ofPattern("yyyyMMdd"));
		System.out.println(result);
		assertEquals("20230618", result);

		result = localDate.format(DateTimeFormatter.ofPattern("yyyy/MM/dd"));
		System.out.println(result);
		assertEquals("2023/06/18", result);
	}

	@Test
	public void parse() {
		LocalDate localDate = LocalDate.parse("2023-06-18");
		System.out.println(localDate);
		assertEquals("2023-06-18", localDate.toString());

		localDate = LocalDate.parse("20230618", DateTimeFormatter.ofPattern("yyyyMMdd"));
		System.out.println(localDate);
		assertEquals("2023-06-18", localDate.toString());

		localDate = LocalDate.parse("2023/06/18", DateTimeFormatter.ofPattern("yyyy/MM/dd"));
		System.out.println(localDate);
		assertEquals("2023-06-18", localDate.toString());
	}
	
	@Test
	public void from() {
		LocalDate localDate = LocalDate.parse("2023-06-18");
		LocalDate result = LocalDate.from(localDate);
		System.out.println(result);
		assertEquals("2023-06-18", result.toString());

		LocalDateTime localDateTime = LocalDateTime.parse("2023-06-18T09:12:05");
		ZoneOffset zoneOffset = ZoneOffset.of("+05:00");
		OffsetDateTime offsetDateTime = OffsetDateTime.of(localDateTime, zoneOffset);
		System.out.println(offsetDateTime);
		result = LocalDate.from(offsetDateTime);
		System.out.println(result);
		assertEquals("2023-06-18", result.toString());

		ZonedDateTime zonedDateTime = ZonedDateTime.parse("2023-06-18T09:12:05+05:00[America/Chicago]");
		result = LocalDate.from(zonedDateTime);
		System.out.println(result);
		assertEquals("2023-06-18", result.toString());
	}

	@Test
	public void toEpochDay() {
		LocalDate localDate = LocalDate.of(2023, 6, 18);
		long result = localDate.toEpochDay();
		System.out.println(result);
		assertEquals(19526L, result);
	}

	@Test
	public void ofEpochDay() {
		LocalDate localDate = LocalDate.ofEpochDay(19526L);
		System.out.println(localDate);
		assertEquals("2023-06-18", localDate.toString());
	}
	
	@Test
	public void ofYearDay() {
		LocalDate localDate = LocalDate.ofYearDay(2023, 169);
		System.out.println(localDate);
		assertEquals("2023-06-18", localDate.toString());
	}
}