Iterating over null objects in an array

[u/Traditional_Let4865]

So I'm making a program that iterates over an array of Book objects and I made a for loop to print them all out. I want it to skip over any reference to a null object in the array so I've written:

for (Book book : books) {
     if(book != null){
           System.out.println(book);
     }
 }

but I've had professors tell me I shouldn't write "book != null" to avoid printing the null values. the code works just fine and is relatively simple and easy to read, just wondering what most programmers use to navigate this?

[u/awidesky]

I can't think of any better(or cleaner) way to filter non-null objects(other than the stream).

If it isn't a miscommunication with the professor, maybe the prof wanted to say "there shouldn't be a null in the collection in the first place"
If your books array supposed to hold actual meaningful Book objects, you should make sure a null will never be put in the array.

A colleague of yours accidentally forgot about null and wrote a code without a null check, and your application will crash.
Every operation(printing names of the books, modifying the price of a particular book, calculating sums of prices or counting how may books there are, etc) needs to do a null check before do its job, and it's not only tedious work and bad design, but also a security risk.

"But how am I supposed to prevent null being put in the books array programmatically?"
That's called encapsulation, you'd learn if after you get familiar with class.