How to make an Integer instance not nullable

Question

Is there a way to ensure an Integer variable not to be null?

I need to create a list of integer values, so I cannot use int type. I need to work with a List<Integer> but this will allow null values for elements...

Do I need to use some particular implementation of List or is there some way to set Integer not nullable?

Note I need a List, not a Set.

Why don't you create your own List class that forbid having a `null` value ? — Kabulan0lak, Jun 10 '14 at 08:12
Obviously, we don't want to reinvent any wheels. However, not *all* wheels have been invented (or at least in your case, publicly implemented). — ChiefTwoPencils, Jun 10 '14 at 08:17
@ChiefTwoPencils this seems like a very common problem, so it's very strange that nothing exists to solve it without having to implement `MyInteger` class... — davioooh, Jun 10 '14 at 08:28
Seems like one of us should do the rest of us a favor then; huh? — ChiefTwoPencils, Jun 10 '14 at 08:46

score 4 · Answer 1 · answered Jun 10 '14 at 08:12

4

No, there is none. Simplest way is just to add a pre-check:

if (intVal != null) {
  list.add(intVal);
} else {
 // TODO: error handling
}

Anyway you'll have to handle an exception/return-value for your custom Data Structure, which doesn't allow NULLs.

answered Jun 10 '14 at 08:12

Denis Kulagin

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succcubbus · Accepted Answer · 2015-04-17T14:43:20.557

4

You could override the add method of a List and check whether the element is null.

new LinkedList<Integer>() {
    @Override
    public boolean add(Integer e) {
        if(e == null)
            return false;
        return super.add(e);
    }
};

You may need to add this check to the other insertion Methods like add(int pos, E value) or set(int pos, E value).

edited Apr 17 '15 at 14:43

answered Jun 10 '14 at 08:14

succcubbus

874
1
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score 1 · Answer 3 · answered Jun 10 '14 at 09:33

1

Just to complete answers above. In case you are using java8 you can benefit from Optional class.

answered Jun 10 '14 at 09:33

Al1en313

151
6

score 0 · Answer 4 · answered Jun 10 '14 at 08:12

Use a Queue implementation, like LinkedBlockingQueue, many of them don't allow nulls.

Look at http://docs.oracle.com/javase/tutorial/collections/implementations/queue.html

I also recommend you to take a look at Lombok's NonNull annotation:

http://projectlombok.org/features/NonNull.html

Gabriel Ruiu · Answer 5 · 2014-06-10T08:47:17.197

You could try, after populating the List, to filter out the null values using the Google Guava Collections2.filter() method:

    List<Integer> myList = new ArrayList<Integer>();
    myList.add(new Integer(2));
    myList.add(null);
    myList.add(new Integer(2));
    myList.add(new Integer(2));
    myList.add(null);
    myList.add(new Integer(2));

    myList = new ArrayList<Integer>(Collections2.filter(myList, new Predicate<Integer>() {
        @Override
        public boolean apply(Integer integer) {
            return integer != null;
        }
    }));

    System.out.println(myList); //outputs [2, 2, 2, 2]

How to make an Integer instance not nullable

5 Answers5