ADDITIONAL SYSTEM INFORMATION :
Java 9.0.4 -- working
Java 10.0.2 -- fails
Java 16.0.2 -- fails
Eclipse build 20210612-2011
Windows 10, Version 10.0.19042 Build 19042

A DESCRIPTION OF THE PROBLEM :
With Java9, when setting weekOfYear=1 on '2010-01-01', it stays on January 1.
Starting from Java10, it is set one week earlier, to '2009-12-25'.

I could not find any related information on the Java10 release notes, so I assume its a bug.
This affects both Calendar and LocalDate calculation.

REGRESSION : Last worked in version 8

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
compile+run with Java9 -- works
compile+run with Java10+ -- fails


---------- BEGIN SOURCE ----------
import java.time.LocalDate;
import java.time.Month;
import java.time.temporal.TemporalField;
import java.time.temporal.WeekFields;
import java.util.Calendar;
import java.util.Date;
import java.util.Locale;
import java.util.TimeZone;

import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.Test;

public class DateTimeUtilsTest {

@Test
public void testDate() {

System.out.println("-- Date --");
final Calendar cal = Calendar.getInstance(TimeZone.getDefault(), Locale.GERMAN);

cal.setTime(new Date(110, 0, 1));
System.out.println(cal.getTime());

cal.set(Calendar.WEEK_OF_YEAR, 2);
System.out.println(cal.getTime());

Assertions.assertEquals(15, cal.get(Calendar.DAY_OF_MONTH));

}

@Test
public void testLocalDate() {
System.out.println("-- LocalDate --");

LocalDate date = LocalDate.of(2010, Month.JANUARY, 1);
final TemporalField weekOfYearField = WeekFields.of(Locale.GERMAN).weekOfYear();

System.out.println(date);
System.out.println(date.get(weekOfYearField));

date = date.with(weekOfYearField, 2);

System.out.println(date);
System.out.println(date.get(weekOfYearField));

Assertions.assertEquals(15, date.getDayOfMonth());
}
}

---------- END SOURCE ----------

FREQUENCY : always