Java中的 TemporalAdjusters firstInMonth() 方法及示例

TemporalAdjusters 类的firstInMonth(DayOfWeek)方法用于返回一个 TemporalAdjuster 对象，该对象可用于获取一个新的 Date 对象，该对象是同月的第一个日期，具有与任何 Date 对象作为参数传递的相同匹配的 DayOfWeek应用此 TempotralAdjuster。

句法：

public static TemporalAdjuster
       firstInMonth(DayOfWeek dayOfWeek)

参数：此方法接受dayOfWeek可用于获取新的 Date 对象，该对象是具有相同匹配 DayOfWeek 的同一月份的第一个日期。

返回值：此方法返回月份调整器中的第一个，不为空。

下面的程序说明了 TemporalAdjusters.firstInMonth() 方法：
方案一：

// Java program to demonstrate
// TemporalAdjusters.firstInMonth()
  
import java.time.*;
import java.time.temporal.*;
  
public class GFG {
    public static void main(String[] args)
    {
  
        // get TemporalAdjuster with
        // the first in month adjuster
        TemporalAdjuster temporalAdjuster
            = TemporalAdjusters.firstInMonth(
                DayOfWeek.SUNDAY);
  
        // using adjuster for local date time
        LocalDate localDate
            = LocalDate.of(2023, 10, 11);
        LocalDate firstInMonth
            = localDate.with(temporalAdjuster);
  
        // print
        System.out.println(
            "First date in month having"
            + " sunday for localdate "
            + localDate + " is: "
            + firstInMonth);
    }
}

输出：

First date in month having sunday for localdate 2023-10-11 is: 2023-10-01

方案二：

// Java program to demonstrate
// TemporalAdjusters.firstInMonth() method
  
import java.time.*;
import java.time.temporal.*;
  
public class GFG {
    public static void main(String[] args)
    {
  
        // get TemporalAdjuster with
        // the first in month adjuster
        TemporalAdjuster temporalAdjuster
            = TemporalAdjusters.firstInMonth(
                DayOfWeek.TUESDAY);
  
        // using adjuster for local date-time
        LocalDate localDate
            = LocalDate.of(2023, 10, 11);
        LocalDate firstInMonth
            = localDate.with(temporalAdjuster);
  
        // print
        System.out.println(
            "First date in a month having"
            + " TUESDAY for localdate "
            + localDate + " is: "
            + firstInMonth);
    }
}

输出：

First date in a month having TUESDAY for localdate 2023-10-11 is: 2023-10-03

参考：https: Java Java.time.DayOfWeek)