JAVA编写从屏幕上输入一个日期，计算出该日期是该年的第几天

其实Java API就带这个方法:
calendar.get(GregorianCalendar.DAY_OF_YEAR);

这个是我写的:
import static java.lang.System.out;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.GregorianCalendar;

public class DayCounter {

private static final long DAY_IN_MILL_SECOND = 24 * 60 * 60 * 1000L;

private Date zeroOClock(Date date) {
if (date == null)
throw new IllegalStateException("date can't be null");
GregorianCalendar calendar = new GregorianCalendar();
calendar.setTime(date);
calendar.set(GregorianCalendar.HOUR_OF_DAY, 0);
calendar.set(GregorianCalendar.MINUTE, 0);
calendar.set(GregorianCalendar.SECOND, 0);
calendar.set(GregorianCalendar.MILLISECOND, 0);
return calendar.getTime();
}

private int daysBetween(Date end, Date start) {
long millSecondsBetween = Math.abs(z