Get start of a month

import java.util.Calendar;
import java.util.Date;

public class Main {
  public static void main(String[] argv) {
    System.out.println(getStartOfMonth(new Date()));
  }

  public static Date getStartOfMonth(Date day) {
    return getStartOfMonth(day, Calendar.getInstance());
}


public static Date getStartOfMonth(Date day, Calendar cal) {
    if (day == null) day = new Date();
    cal.setTime(day);

    // set time to start of day
    cal.set(Calendar.HOUR_OF_DAY, cal.getMinimum(Calendar.HOUR_OF_DAY));
    cal.set(Calendar.MINUTE,      cal.getMinimum(Calendar.MINUTE));
    cal.set(Calendar.SECOND,      cal.getMinimum(Calendar.SECOND));
    cal.set(Calendar.MILLISECOND, cal.getMinimum(Calendar.MILLISECOND));

    // set time to first day of month
    cal.set(Calendar.DAY_OF_MONTH, 1);

    return cal.getTime();
}
}