Java 8では、あらかじめ定義された `java.time.temporal.TemporalAdjusters`を使用して日付を調整したり、https://docs.oracle.com/javase/8/docs/api/java/time/temporal/Temporal.htmlを調整することができます[時代]

1.時間的調節器

firstDayOfMonth、firstDayOfNextMonth、次の月曜日などに日付を移動する例

TestDate.java 

package com.mkyong.time;

import java.time.DayOfWeek;
import java.time.LocalDate;
import java.time.temporal.TemporalAdjusters;

public class TestDate {

    public static void main(String[]args) {

        LocalDate localDate = LocalDate.now();
        System.out.println("current date : " + localDate);

        LocalDate with = localDate.with(TemporalAdjusters.firstDayOfMonth());
        System.out.println("firstDayOfMonth : " + with);

        LocalDate with1 = localDate.with(TemporalAdjusters.lastDayOfMonth());
        System.out.println("lastDayOfMonth : " + with1);

        LocalDate with2 = localDate.with(TemporalAdjusters.next(DayOfWeek.MONDAY));
        System.out.println("next monday : " + with2);

        LocalDate with3 = localDate.with(TemporalAdjusters.firstDayOfNextMonth());
        System.out.println("firstDayOfNextMonth : " + with3);

    }

}

出力 

current date : 2016-11-15
firstDayOfMonth : 2016-11-01
lastDayOfMonth : 2016-11-30
next monday : 2016-11-21
firstDayOfNextMonth : 2016-12-01

2.カスタムTemporalAdjuster

次のクリスマスに日付を移動するための `TemporalAdjuster`を実装する例

NextChristmas.java 

package com.mkyong.time;

import java.time.temporal.ChronoField;
import java.time.temporal.Temporal;
import java.time.temporal.TemporalAdjuster;

public class NextChristmas implements TemporalAdjuster {

    @Override
    public Temporal adjustInto(Temporal temporal) {

        return temporal.with(ChronoField.MONTH__OF__YEAR, 12).with(ChronoField.DAY__OF__MONTH, 25);

    }
}

TestDate.java 

package com.mkyong.time;

import java.time.LocalDate;

public class TestDate {

    public static void main(String[]args) {

        LocalDate localDate = LocalDate.now();
        System.out.println("current date : " + localDate);

        localDate = localDate.with(new NextChristmas());
        System.out.println("Next Christmas : " + localDate);

    }

}

出力 

current date : 2016-11-15
Next Christmas : 2016-12-25

または、次のラムダ式を使用することもできます。 

    localDate = localDate.with(
        temporal -> temporal.with(ChronoField.MONTH__OF__YEAR, 12).with(ChronoField.DAY__OF__MONTH, 25)
    );

参考文献

  1. リンク://java8/java-8-hijrahdate-how-to-calculate-the-ramadan-date/[Java

8 – HijrahDate、ラマダン日付の計算方法]。

https://docs/

JavaDoc]。

https://docs.oracle.com/javase/8/docs/api/java/time/temporal/TemporalAdjusters.html

[TemporalAdjusters

JavaDoc]。

https://docs.oracle.com/javase/8/docs/api/java/time/temporal/Temporal.html

[Temporal

JavaDoc]。

Wikipediaクリスマス

リンク://タグ/日付/[日付]リンク://タグ/java-time/[java.time]リンク://タグ/java8/[java8]

TemporalAdjusters