public BookRecord(String author, String title, int year, int copies)
{
// Create a new book record, error check everything using exceptions
try {
// Check author is valid
if(author == null || author.length() == 0) {
throw new IOException("No author entered");
} else {
this.author = author;
}
// Check title is valid
if(title == null || title.length() == 0) {
throw new IOException("No Title entered");
} else {
this.title = title;
}
// Get the year and check book isn't from the future
Calendar cal = new GregorianCalendar();
int currentyear = cal.get(Calendar.YEAR);
if(year > currentyear || year < 0) {
throw new IOException("No time travelling books");
} else {
this.year = year;
}
// Check number of copies is valid
if(copies < 0) {
throw new IOException("Too few copies");
} else {
this.copies = copies;
}
} catch(IOException e) {
// If we have an error, print it
System.out.println("Error Creating Book Record: " + e.getMessage());
System.out.println();
}
}
Code sample 2: The BookRecord constructor
Code reprinted from the .java document on this specific lab (BookRecord.java by Joao R. Goncalves)
This code sample uses Java exception handling to keep track of possible errors, for later debugging, if necessary. The other methods in the class were simple accessor methods designed to return the value contained in a specific field. For example, methods such as getAuthor(), getTitle() and getYear() returned the author name, title of the book and year of publication, respectively. This makes it possible for other classes to access the information of the one in question, without allowing them to edit or delete the values of the fields (unless we instruct the fields to be “editable” by other classes, by making them public instead of private).
3. The Library class
In this class we want to store all the books, be able to edit or delete them, as well as print information regarding those books. For the purpose of managing the books in the library created an ArrayList where we could add the books using the method addBookRecord(). This method took four parameters in order to create a Book object and add it to the list. We would also like to get all of the books printed out, so a listAllBooks() method was implemented, which would present us with the list in case there were any books inserted. To print all the records a for-loop was used to iterate through the ArrayList and print its details.
The big challenge was to create a method to search the list for a specific book, or a book by a particular author. Named as queryBookList, this new method would take either one or two string parameters, according to whether the user wanted to search for just an author or book, or both of them. Once again, a for-loop was implemented to go through all the book records and return us the details of the books matching the values inputted by the user. In case a book was to be found by its title, the method would only try to match the title entered with the ones in the book list, and the same applies if the user wanted to search by author. This is ensured by the if-statements in the code for this class (See Code Sample 2). If one or more books are found, the details for each one of them are printed to the screen. On the other hand, if no books match the search criteria a message appears: (“Books found: ” followed by “None.”). The code for this class is as follows:
import java.io.*;
import java.lang.*;
import java.util.*;
public class Library
{
ArrayList booklist;
/**
* Constructor for objects of class Library
*/
public Library()
{
booklist = new ArrayList();
}
/**
* Add a book to the library
* @param author The author of the book
* @param title The title of the book
* @param year The year the book was published
* @param copies The number of copies in stock
* @return a reference to the BookRecord
*/
public BookRecord addBookRecord(String author, String title, int year, int copies)
{
BookRecord book = new BookRecord(author, title, year, copies);
booklist.add(book);
return book;
}
/**
* List all the books
*/
public void listAllBooks()
{
// Check we have books
if(booklist.size() == 0) {
System.out.println("No books on file.");
System.out.println("");
return;
}
// Print all the books
System.out.println("Books found:");
for(int i=0; i<booklist.size(); i++)
{
BookRecord book = (BookRecord)booklist.get(i);
book.printDetails();
}
System.out.println(booklist.size() + " books on file.");
System.out.println();
}
/**
* Query for a book based on author or title
*
* @param author The author of the book, null to not search for this
* @param title The title of the book, null to not search for this
*/
public void queryBookList(String author, String title)
{
// Print header
System.out.println("Books found:");
int booksfound = 0;
for(int i=0; i<booklist.size(); i++)
{
// Get the book
boolean found = true;
BookRecord book = (BookRecord)booklist.get(i);
// If author is specified, check equality
if(author != null)
if(book.getAuthor() != author)
found = false;
// If title is specified, check equality
if(title != null)
if(book.getTitle() != title)
found = false;
// If both tests have been passed, print book
if(found)
{
book.printDetails();
booksfound++;
}
}
// Print footer
if(booksfound == 0)
System.out.println("None.");
System.out.println("End of query.");
System.out.println();
}
}
Code sample 2: The Library Class
Code reprinted from the .java document on this specific lab (Library.java by Joao R. Goncalves)
Some tests were run after the library class was complete, in order to determine if these were working properly. These included adding records to the book list, and then printing them to the screen, as well as searching the list for a specific book or author. To carry out these functionality tests, some books were added to the Library using the addBookRecord(), and then the listAll() method was executed, which printed the results in Figure 2. The queryBookList method was then called, to retrieve the books written by the author Peter Grossman, and the output can be checked in Figure 3. The images of the results of the tests are available below:
Figure 2: The list of books in the ArrayList
Figure 3: The search results for books by Peter Grossman
4. Conclusions
The laboratory session provided useful knowledge on the use of data collection objects such as ArrayList’s, as well as methods to iterate through them in order to retrieve data. Also, the interaction between objects becomes clearer, as it is the main idea behind object-oriented programming languages such as Java or C++.
5. References
COMP1004 – Programming Principles lab 3 challenge specifications on project B. Viewed on 28-10-04 at
