title: writing a public int compareTo() method java
body: <p>I have an assignment where I need to create an arraylist of BookInventory objects with params (String bookNum, String bookTitle, int qoh, double bookPrice).  Where bookNum is the hyphenated ISBN number of a book.  After creating this array, I need to use the sort method of the Collections class.  In my entity BookInventory class, I need to write a compareTo() that will end up sorting the arraylist by bookNum (which is a String).  How do I do this?  This is my first experience with this, and I don't understand.  </p>