public final class Period {
  private final Date start;
  private final Date end;
  
  public Period(Date start, Date end) {
    this.start = new Date(start.getTime());
    this.end = new Date(end.getTime());
    if (this.start.compareTo(this.end) > 0)
      throw new IllegalArgumentException(start + "after" + end); 
  }
  
  public Date start() {
    return new Date(start.getTime()); 
  }

  public Date end() {
    return new Date(end.getTime());
  }
}

public class BogusPeriod {
	//진짜 Period 인스턴스에서는 만들어질 수 없는 바이트 스트림
	private static final byte[] serializedForm = new byte[] { (byte) 0xac,
			(byte) 0xed, 0x00, 0x05, 0x73, 0x72, 0x00, 0x06, 0x50, 0x65, 0x72,
			0x69, 0x6f, 0x64, 0x40, 0x7e, (byte) 0xf8, 0x2b, 0x4f, 0x46,
			(byte) 0xc0, (byte) 0xf4, 0x02, 0x00, 0x02, 0x4c, 0x00, 0x03, 0x65,
			0x6e, 0x64, 0x74, 0x00, 0x10, 0x4c, 0x6a, 0x61, 0x76, 0x61, 0x2f,
			0x75, 0x74, 0x69, 0x6c, 0x2f, 0x44, 0x61, 0x74, 0x65, 0x3b, 0x4c,
			0x00, 0x05, 0x73, 0x74, 0x61, 0x72, 0x74, 0x71, 0x00, 0x7e, 0x00,
			0x01, 0x78, 0x70, 0x73, 0x72, 0x00, 0x0e, 0x6a, 0x61, 0x76, 0x61,
			0x2e, 0x75, 0x74, 0x69, 0x6c, 0x2e, 0x44, 0x61, 0x74, 0x65, 0x68,
			0x6a, (byte) 0x81, 0x01, 0x4b, 0x59, 0x74, 0x19, 0x03, 0x00, 0x00,
			0x78, 0x70, 0x77, 0x08, 0x00, 0x00, 0x00, 0x66, (byte) 0xdf, 0x6e,
			0x1e, 0x00, 0x78, 0x73, 0x71, 0x00, 0x7e, 0x00, 0x03, 0x77, 0x08,
			0x00, 0x00, 0x00, (byte) 0xd5, 0x17, 0x69, 0x22, 0x00, 0x78 };

	public static void main(String[] args) {
		Period p = (Period) deserialize(serializedForm);
		System.out.println(p);
	}

	// 주어진 직렬화 형태(바이트 스트림)로부터 객체를 만들어 반환한다.
	private static Object deserialize(byte[] sf) {
		try {
			InputStream is = new ByteArrayInputStream(sf);
			ObjectInputStream ois = new ObjectInputStream(is);
			return ois.readObject();
		} catch (Exception e) {
			throw new IllegalArgumentException(e);
		}
	}
}

private void readObject(ObjectInputStream s) throws IOException, ClassNotFoundException {
  
  //불변식을 만족하는지 검사한다.
  if (start.compareTo(end) > 0) 
    throw new InvalidObjectException(start +" after " + end);
}

public class MutablePeriod {
	// Period 인스턴스
	public final Period period;

	// 시작 시각 필드
	public final Date start;

	// period's end field, to which we shouldn't have access
	public final Date end;

	public MutablePeriod() {
		try {
			ByteArrayOutputStream bos = new ByteArrayOutputStream();
			ObjectOutputStream out = new ObjectOutputStream(bos);

			// Serialize a valid Period instance
			out.writeObject(new Period(new Date(), new Date()));

			/*
			 * Append rogue "previous object refs" for internal Date fields in
			 * Period. For details, see "Java Object Serialization
			 * Specification," Section 6.4.
			 */
			byte[] ref = { 0x71, 0, 0x7e, 0, 5 }; // Ref #5
			bos.write(ref); // The start field
			ref[4] = 4; // Ref # 4
			bos.write(ref); // The end field

			// Deserialize Period and "stolen" Date references
			ObjectInputStream in = new ObjectInputStream(
					new ByteArrayInputStream(bos.toByteArray()));
			period = (Period) in.readObject();
			start = (Date) in.readObject();
			end = (Date) in.readObject();
		} catch (Exception e) {
			throw new AssertionError(e);
		}
	}
}

private void readObject(ObjectInputStream s) throws IOException, ClassNotFoundException {
  s.defaultReadObject();
  
  //가변 요소들을 방어적으로 복사한다.
  start = new Date(start.getTime());
  end = new Date(end.getTime());
  
  // 불변식을 만족하는지 검사한다.
  if (start.compareTo(end) > 0)
    throw new InvalidObjectException(start +" after " + end);
}