Java program runtime error

Your allocation of MyBooks[3] only assigns the array You still need to assign a "new MyBook()" to each entry in your array.

look at your line:

Books [] myBooks = new Books[3]; 

you create an array, although every element in the array is a null pointer.

Saw it, you need to initializate each one of the elments of your array, try it with in an for or a while

This should work :

public class BooksTestDrive { public static void main(String[] args) { Books [] myBooks = new Books[3]; // init loop for (int i=0;i<myBooks.length;i++) { myBooks[i] = new Books(); } myBooks[0].title = "The Grapes of Jave"; myBooks[1].title = "The Java Gatsby"; myBooks[2].title = "The Java Cookbook"; myBooks[0].author = "bob"; myBooks[1].author = "sue"; myBooks[2].author = "ian"; for (Books book : myBooks) { System.out.printf("%s by %s\n",book.title,book.author); } } } } 

You need to add the books to the arrays. This should work:

class BooksTestDrive { public static void main(String [] args) { Books [] myBooks = new Books[3]; int x = 0; // THIS IS WHAT WAS MISSING. myBooks[0] = new Books(); myBooks[1] = new Books(); myBooks[2] = new Books(); myBooks[0].title = "The Grapes of Java"; myBooks[1].title = "The Java Gatsby"; myBooks[2].title = "The Java Cookbook"; myBooks[0].author = "bob"; myBooks[1].author = "sue"; myBooks[2].author = "ian"; while (x < 3) { System.out.print(myBooks[x].title); System.out.print(" by "); System.out.println(myBooks[x].author) ; x = x + 1; } } }