How to add a new entry to array?

Question

For this project, I can remove only the top one from the pile, and cannot remove a book from under another one. Likewise, I cannot add a book beneath another one. I can add another book to the pile only by placing it on the top of the pile. In my code, I removed Book E from the pile, but now I want to add a different book. How to add a new book (Book: F) to myBooks and print the list? There is a link to the screenshot of my current output.

screenshot of current output

public class Driver
{
    public static void main(String[] args)
    {
        Book[] myBooks = { new Book("A"), new Book("B"), new Book("C"), new Book("D"), new Book("E")};
        PileOfBooksInterface<Book> bookPiles = new PileOfBooks<>();
        System.out.println("Are there any books in the pile? " + bookPiles.isEmpty());

        for (int index = 0; index < myBooks.length; index++)
        {
            Book nextItem = myBooks[index];
            bookPiles.add(nextItem);
        } // end for

        System.out.println("\nTotal books in the pile:");

        for (int index = 0; index < myBooks.length; index++) 
        {
            System.out.println(myBooks[index]);
        } // end for

        System.out.println("\nRemoving the last book:");
        bookPiles.remove();
        Object[] arr = (bookPiles.toArray());

        for (int index = 0; index < arr.length; index++) 
        {
            System.out.println(arr[index]);
        } // end for

        System.out.println("\nAdding new book on top of the pile:");
         // ???

    }
}

Answer 1

It's simple. You can use ArrayList to store all your books and java have pretty nice inbuilt methods for ArrayList. You can do something as below:

public class Driver
{
    public static void main(String[] args)
    {
        Book[] myBooks = { new Book("A"), new Book("B"), new Book("C"), new Book("D"), new Book("E")};
        ArrayList<Book> bookPiles = new ArrayList<Book>();
        System.out.println("Are there any books in the pile? " + bookPiles.isEmpty());

        for (int index = 0; index < myBooks.size(); index++)
        {
            Book nextItem = myBooks[index];
            bookPiles.add(nextItem);//populating ArrayList
        } // end for

        System.out.println("\nTotal books in the pile:");

        for (int index = 0; index < myBooks.size(); index++) 
        {
            System.out.println(bookPiles.get(index));
        } // end for

        System.out.println("\nRemoving the last book:");
        bookPiles.remove(bookPiles.size()-1); //removing the last element from the bookPile ArrayList
        //Object[] arr = (bookPiles.toArray()); //No need for this line

        for (int index = 0; index < bookPiles.size(); index++) 
        {
            System.out.println(bookPiles.get(index));
        } // end for

        System.out.println("\nAdding new book on top of the pile:");
         // you can write the code for adding at the top of the pile as follows:

        bookPiles.add(0,new Book("E"));//0 is the first position in the ArrayList where we want to add data and all the elements will be shifted automatically.
        //the above line will add the new book at the top of the pile.
        for (int index = 0; index < bookPiles.size(); index++) 
        {
            System.out.println(bookPiles.get(index)); //print all the books along with the new one
        } 


    }
}

Hope this helps you.

Answer 2

With a stack you no longer need a pile of books class and will work the way you expect it to.

public class Driver {
    public static void main(String[] args) {
        Stack<Book> bookPiles = Arrays.asList(new Book("A"), new Book("B"), new Book("C"), new Book("D"), new Book("E")).stream()
            .collect(Collectors.toCollection(Stack::new));
        System.out.println("Are there any books in the pile? " + !bookPiles.isEmpty());
        System.out.println("\nTotal books in the pile:");
        bookPiles.stream().forEach(System.out::println);
        System.out.println("\nRemoving the last book:");
        bookPiles.pop();
        bookPiles.stream().forEach(System.out::println);
        System.out.println("\nAdding new book on top of the pile:");
        bookPiles.push(new Book("F"));
        bookPiles.stream().forEach(System.out::println);
    }
}

If PileOfBooks is already written and is known to work as you describe, then you would only need to add a book to the PileOfBooks like you did when adding the books to begin with.

bookPiles.add(new Book("F"));