Question

Iam writing a simple Java program for an assignment,which implements a library system using inheritance.I have a class named Entry and two others who extend it (book and journal).

Everything works fine.

Now i must create a class which will test the whole program.This class should use an array to store the elements (books OR journals which i want to add in the system).I don’t know how many elements i will add but i must declare an array for them (either my entry will be book,or journal).My question is:This array should be an Entry array (as i suppose) and if yes,if for example i want to add a book the extra elements that Book has where will be stored?

Thank you in advance.

Answer 1

Yes you should add to an Entry array. You can add Book instance to the Entry array since it is extending Entry. To access the properties or methods of Book after getting it from Entry array, you have to cast it to Book.

Entry[] entries = new Entry[5];
entries[0] = new Book();
Book aBook = (Book)entries[0];
aBook.getBookTitle();