Method addBook

java/Chapter 8/Question8_5/Library.java:9–16

(int id, String details)

	private Hashtable<Integer, Book> books;
	
	public Book addBook(int id, String details) {
		if (books.containsKey(id)) {
			return null;
		}
		Book book = new Book(id, details);
		books.put(id, book);
		return book;
	}
	
	public boolean remove(Book b){
		return remove(b.getID());