Help with constructors

[philip1597]

Hello all,
I am having figuring out how to make my code add the objects(books) listed in the main to my array. Any help would be Appreciated.

package book.pkg;
public class Book {
    String title;
    boolean borrowed;

    // Creates a new Book
    public Book(String bookTitle) {
        title = bookTitle;
        // Implement this method
    }

    // Marks the book as rented
    public void rented() {
        // Implement this method
        borrowed = true;
    }

    // Marks the book as not rented
    public void returned() {
        // Implement this method
        borrowed = false;
    }

    //
    // Returns true if the book is rented, false otherwise
    public boolean isBorrowed() {
        // Implement this method
        //rented();
        //returned();
        
        return borrowed;
    }
    //public boolean notBorrowed(){
        
    //}
    // Returns the title of the book
    public String getTitle() {
        // Implement this method
        return title;
    }

    //
    public static void main(String[] arguments) {
        // Small test of the Book class
        Book example = new Book("The Da Vinci Code");
        System.out.println("Title (should be The Da Vinci Code): "
                + example.getTitle());
        System.out.println("Borrowed? (should be false): "
                + example.isBorrowed());
        example.rented();
        System.out.println("Borrowed? (should be true): "
                + example.isBorrowed());
         example.returned();
        System.out.println("Borrowed? (should be false): "
                + example.isBorrowed());
    }


    }

import book.pkg.Book;

public class Library {
	Book[] books = new Book[3];
	Object firstLibrary;
	Object secondLibrary;
	//Constructors for two libraries
	Library (String address1) {
		firstLibrary = address1;
	}

	Library(String address1, String address2) {
		secondLibrary = address2;
	}
	//Add certain books to libraries
	public Book[] addBook(Book book) {
		books[0] = book;
		books[1] = book;
		books[2] = book;
		books[3] = book;
		return books;
	}

	public static void printOpeningHours() {
		System.out.println("Libraries are open daily from 9 AM to 5 PM");
	}

	public void printAddress() {
		System.out.println(firstLibrary);
		System.out.println(secondLibrary);
	}
	//Remove certain books from libraries
	public Book[] borrowBook(String Book) {
		return books;
	}
	//Print books in Libraries
	public void printAvailableBooks() {

	}
	//Re-add Borrowed books
	public String returnBook(String Book) {
		return Book;
	}

	public static void main(String[] args) {

		// Create two libraries
		Library firstLibrary = new Library("10 Main St.");
		Library secondLibrary = new Library("228 Liberty St.");
		// Add four books to the first library
		firstLibrary.addBook(new Book("The Da Vinci Code"));
		firstLibrary.addBook(new Book("Le Petit Prince"));
		firstLibrary.addBook(new Book("A Tale of Two Cities"));
		firstLibrary.addBook(new Book("The Lord of the Rings"));
		// Print opening hours and the addresses
		System.out.println("Library hours:");
		printOpeningHours();
		System.out.println();
		System.out.println("Library addresses:");
		firstLibrary.printAddress();
		secondLibrary.printAddress();
		System.out.println();
		// Try to borrow The Lords of the Rings from both libraries
		System.out.println("Borrowing The Lord of the Rings:");
		firstLibrary.borrowBook("The Lord of the Rings");
		firstLibrary.borrowBook("The Lord of the Rings");
		secondLibrary.borrowBook("The Lord of the Rings");
		System.out.println();
		// Print the titles of all available books from both libraries
		System.out.println("Books available in the first library:");
		firstLibrary.printAvailableBooks();
		System.out.println();
		System.out.println("Books available in the second library:");
		secondLibrary.printAvailableBooks();
		System.out.println();
		// Return The Lords of the Rings to the first library
		System.out.println("Returning The Lord of the Rings:");
		firstLibrary.returnBook("The Lord of the Rings");
		System.out.println();
		// Print the titles of available from the first library
		System.out.println("Books available in the first library:");
		firstLibrary.printAvailableBooks();
	}
}

[Tolls]

What problem are you having?
That is, what are you seeing happen with your code and what do you think you should be seeing?

[philip1597]

The code is giving me an error when there aren't any visible errors. I would expect it would at least add one object to the array. It gives me the error "Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 3
at Library.addBook(Library.java:20)
at Library.main(Library.java:51)"

[Fubarable]

The error makes sense, and let's look at your code to see why:

    Book[] books = new Book[3]; //  ************** line 1
    Object firstLibrary;
    Object secondLibrary;
    //Constructors for two libraries
    Library (String address1) {
        firstLibrary = address1;
    }
 
    Library(String address1, String address2) {
        secondLibrary = address2;
    }
    //Add certain books to libraries
    public Book[] addBook(Book book) {
        books[0] = book;
        books[1] = book;
        books[2] = book;
        books[3] = book; //  ************** line 2
        return books;
    }

Notice that on line 1 you declare an array, books that is initialized to hold Book objects. Then on line 2 you give it a 4th Book object. The error not only tells you exactly what is wrong -- array index is out of bounds, but it likely will tell you which line is causing it, line 20 which is probably the line 2 that I commented above. Solution, if you need an array to hold 4 items, then initialize it to hold 4 items.

Also note that your addBook(...) method is wrong. It adds the same Book item into the array 4 times, and I doubt that's what you want to do.

[philip1597]

You were right I expanded the array and the error was fixed, but wouldn't declaring it as [3] make it length 4 because arrays start at 0? and I know method addbook won't work I just put something there as a placeholder until I figure out what I should be putting there.

[Fubarable]

You were right I expanded the array and the error was fixed, but wouldn't declaring it as [3] make it length 4 because arrays start at 0?

Nope.

An array declared with 3 items will hold 3 items, with indices 0, 1, and 2. Since arrays are zero-based, they will go up to index (length - 1).

and I know method addbook won't work I just put something there as a placeholder until I figure out what I should be putting there.

Fair enough.

[philip1597]

Thank you very much for the help.

[Fubarable]

You're quite welcome!