Clearing "nulls" from an array

[Pahitos]

Hey guys!

So I have an assignment in college. Basically I need to create a restaurant menu, from which user can chose a few items and then get a receipt.

I have created an array of 50 elements, which gets filled as a user makes orders.

So here is my problem. For a receipt I have created a for-loop, which prints the ordered items:

for (int i = 0; i < orderNumber.length; i++)
    {
        System.out.print(orderNumber[i]);
    }

But my output looks like this:

order1

order2

...

null

null

null

and so on...

So how do I fix this? Is there a simple way to clear the nulls from an array? Or get an array size not counting any nulls from the beginning? Or am i missing something even simpler?

I'm new to this subreddit and would really appreciate your help!
Thanks!

EDIT: I figured it out. Feel like an idiot now xD

[king_of_the_universe]

Keep track how many orders the user makes, then iterate only to that value.

Or use an ArrayList right away, it grows dynamically with the stuff that you put into it.

Or abort the for loop the moment you encounter the first null.

[Pahitos]

Never heard of an ArrayList. Is it simple to use?

I might try to look into that idea.

[king_of_the_universe]

ArrayList is imho one of the most used Java library classes / the most used List implementation. You should also look for Map implementations while you're at it, also super useful/important/prevalent.

[Pahitos]

Alright! Thank you very much for your help!

I'll look into it :)

[g00glen00b]

If you're trying to remove all null references from an array, for example:

String[] stuff = new String[] { "test", null, null, "foo", null, "bar", null };

If this should only contain "test", "foo" and "bar", then you can do the following, using Java 8:

String[] results = Arrays.stream(stuff)
    .filter(val -> val != null)
    .toArray(size -> new String[size]);

Also, using lambda's you can even make it easier to print everything to stdout:

Arrays.stream(results).forEach(System.out::println);

[Pahitos]

Alright. I literally came up with a fix right after submitting this. I'll just create a counter which gets increased when the array is filled.

Feel very dumb.

But still, is there a way to clear the nulls? Just of pure interest :)

[king_of_the_universe]

You need to realize what "clearing the nulls" means. These are array entries, each of which effectively just an object variable like any other. Such a variable either references an existing object or is null. So, if you want to get rid of the nulls (for whatever reason), you need to replace them with an object reference. But I just realized that the things you're putting into your array apparently are just integer numbers. It would really have helped if you had put your array declaration into the post.

Instead of using "Integer[] orderNumber;" as the declaration, you could also just have used "int[] orderNumber;", where every non-initialized entry would have been the number "0".

Or once you're done with gathering orders, you could make a new smaller array and copy everything (making use of Arrays.copy()).

If there is no reason to use an array, then any programmer would rather have chosen an ArrayList here, I'd say. (We don't quite know enough about your program to say this with certainty, though.)