如何添加新条目到数组？

Question

对于这个项目，我只能从书堆中删除最上面的一本书，而不能从另一本书的下面删除一本书。 同样，我不能在另一本书下面添加一本书。 我只能将另一本书放在书堆的顶部，才能将其添加到书堆中。 在我的代码中，我从书堆中删除了Book E，但是现在我想添加另一本书。 如何将新书（书号：F）添加到myBooks并打印列表？ 有一个指向我当前输出的屏幕截图的链接。

当前输出的屏幕截图

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

使用一a书，您不再需要一堆书课，并且可以按您期望的方式工作。

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);
    }
}

如果已经编写了PIleOfBooks，并且可以按照您所描述的那样工作，那么您只需像在添加书本时那样将一本书添加到PileOfBooks中即可。

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

Answer 2

这很简单。 您可以使用ArrayList来存储所有书籍，而Java具有ArrayList的漂亮内置方法。 您可以执行以下操作：

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
        } 


    }
}

希望这对您有所帮助。