Adding null values to arraylist

Question

Can I add null values to an ArrayList even if it has a generic type parameter?

Eg.

ArrayList<Item> itemList = new ArrayList<Item>();
itemList.add(null);

If so, will

itemsList.size();

return 1 or 0?

If I can add null values to an ArrayList , can I loop through only the indexes that contain items like this?

for(Item i : itemList) {
   //code here
}

Or would the for each loop also loop through the null values in the list?

Answer 1

Yes, you can always use null instead of an object. Just be careful because some methods might throw error.

It would be 1.

Also null s would be factored in in the for loop, but you could use

for (Item i : itemList) {
    if (i != null) {
       //code here
    }
}

Answer 2

You can add nulls to the ArrayList , and you will have to check for nulls in the loop:

for(Item i : itemList) {
   if (i != null) {

   }
}

itemsList.size(); would take the null into account.

 List<Integer> list = new ArrayList<Integer>();
 list.add(null);
 list.add (5);
 System.out.println (list.size());
 for (Integer value : list) {
   if (value == null)
       System.out.println ("null value");
   else 
       System.out.println (value);
 }

Output :

2
null value
5

Answer 3

You could create Util class:

public final class CollectionHelpers {
    public static <T> boolean addNullSafe(List<T> list, T element) {
        if (list == null || element == null) {
            return false;
        }

        return list.add(element);
    }
}

And then use it:

Element element = getElementFromSomeWhere(someParameter);
List<Element> arrayList = new ArrayList<>();
CollectionHelpers.addNullSafe(list, element);