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?
Yes, you can always use null instead of an object. Just be careful because some methods might throw error.
It would be 1.
Also nulls would be factored in in the for loop, but you could use
for (Item i : itemList) {
if (i != null) {
//code here
}
}
List.of(...) will throw if the supplied value is null. This is dumb -- just putting it out there. It's perfectly legit to have a null value in a list!
List.of(...) will throw exception however Stream.of(null, "a").toList() works perfectly fine.
Collections.singletonList() does allow null, which means that the of method is even more "off". Anyway, if you need to create a list of one element that may be null then singletonList may help.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
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);
