RMI – implementation of the library book

import java.util.*;
import java.rmi.*;
import java.rmi.server.*;
 
// UnicaseRemoteObject = remote object classes need to implement the related
// remote interface
public class Book extends UnicastRemoteObject implements Borrowable {
	private Date borrowDate;
	private Date returnDate;
	private String borrowerID;
	private String title;
	private boolean checkedOut = false;
 
	// create book.
	public Book (String bookName) throws RemoteException
	{
		title = bookName;
	}
 
	// is the book already checked out ?
	public boolean isCheckedOut() throws RemoteException
	{
		return checkedOut;
	}
 
	// if the book is checked out, return the library card number + date it was taken out on
	public String checkedOutCardNumber() throws RemoteException
	{
		String returnID = null;
		if (isCheckedOut())
		{
			returnID = borrowerID + " Date taken out on "+ borrowDate.toString();
		}
		return returnID;
	}
 
	public boolean checkOut(String cardNumber, Date d ) throws RemoteException
	{
		// do not check out the book if already checked out!
		if (isCheckedOut())
			return false;
		borrowerID = cardNumber;
		borrowDate = d;
		checkedOut = true;
		return true;
	}
 
	public boolean checkIn(String cardNumber, Date d) throws RemoteException
	{
		// if it is checked out, check the book in.
		if (isCheckedOut())
		{
			borrowerID = cardNumber;
			returnDate = d;
			checkedOut = false;
			return true;
		}
		return false;
	}
}