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;
        }
    }
}