又一道来外的面试题，据说要提防陷阱

Create a "Diary" class that has a collection of appointments, and has a method that returns the first available slot after the current time of a given duration.

我怎么感觉更像作业呢？

import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;

public class Helper {
	public static Calendar getCalendarFromString(String str) {
		Date date = null;
		try {
			SimpleDateFormat formatter = new SimpleDateFormat("yyyyMMddHHmmss");
			date = formatter.parse(str);
		} catch (Exception e) {
			e.printStackTrace();
		}
		Calendar calendar = Calendar.getInstance();
		calendar.setTime(date);
		return calendar;
	}
}

import java.util.Calendar;

public class Appointment {
	private Calendar startTime;
	private Calendar endTime;
	private String content;

	Appointment(String startTimeStr, String endTimeStr, String content) {
		Calendar startTime = Helper.getCalendarFromString(startTimeStr);
		Calendar endTime = Helper.getCalendarFromString(endTimeStr);
		if (startTime.compareTo(endTime) >= 0) {
			throw new RuntimeException(
					"error: StartTime should before EndTime!");
		}
		this.startTime = startTime;
		this.endTime = endTime;
		this.content = content;
	}

	public Calendar getStartTime() {
		return startTime;
	}

	public Calendar getEndTime() {
		return endTime;
	}

	public String getContent() {
		return content;
	}

	public String toString() {
		return "StartTime:" + startTime.getTime() + "\nEndTime:"
				+ endTime.getTime() + "\nContent:" + content;
	}
}

import java.util.ArrayList;
import java.util.Calendar;
import java.util.GregorianCalendar;
import java.util.List;

public class Diary {
	private List<Appointment> appointmentList = new ArrayList<Appointment>();

	private Calendar start;

	private Calendar end;

	Diary(String day) {
		this.start = Helper.getCalendarFromString(day + "000000");
		this.end = Helper.getCalendarFromString(day + "240000");
	}

	public void add(Appointment appointment) {
		int index = -1;
		if (appointment.getStartTime().before(this.start)
				|| appointment.getEndTime().after(this.end)) {
			throw new RuntimeException("the day of the appointment should be:"
					+ start.getTime() + " which Diary specified");
		}
		int size = appointmentList.size();
		if (size == 0) {
			index = 0;
		} else {
			for (int i = 0; i < size; i++) {
				Calendar startTimeExist = appointmentList.get(i).getStartTime();
				Calendar endTimeExist = appointmentList.get(i).getEndTime();
				Calendar startTime = appointment.getStartTime();
				Calendar endTime = appointment.getEndTime();
				if (endTime.compareTo(startTimeExist) <= 0) {
					index = i;
					break;
				} else if (startTime.compareTo(endTimeExist) < 0) {
					throw new RuntimeException(
							"error: time has already occupied");
				} else {
				}
			}
			index = index == -1 ? size : index;
		}
		this.appointmentList.add(index, appointment);
	}

	public Appointment getComingAppointment() {
		Appointment result = null;
		for (int i = 0; i < this.appointmentList.size(); i++) {
			Appointment appointment = appointmentList.get(i);
			if (new GregorianCalendar().compareTo(appointment.getStartTime()) < 0) {
				result = appointment;
				break;
			}
		}
		return result;
	}

	public static void main(String[] args) {
		Diary diary = new Diary("20080620");
		Appointment app1 = new Appointment("20080620010000", "20080620020000",
				"item1");
		Appointment app2 = new Appointment("20080620130000", "20080620140000",
				"item2");
		Appointment app3 = new Appointment("20080620150000", "20080620160000",
				"item3");
		Appointment app4 = new Appointment("20080620160000", "20080620170000",
				"item4");
		Appointment app5 = new Appointment("20080620180000", "20080620190000",
				"item5");
		Appointment app6 = new Appointment("20080620230000", "20080620240000",
				"item6");
		diary.add(app6);
		diary.add(app5);
		diary.add(app2);
		diary.add(app3);
		diary.add(app1);
		diary.add(app4);
		Appointment result = diary.getComingAppointment();
		System.out.println(result);

	}
}

就这句话a method that returns the first available slot after the current time of a given duration.举个例子：
你现在有个1个小时的会议要安排，这个method应该返回一个空余的时间段给此会议。