Ways to check if an ArrayList contains only null values

Question

I was looking through the code for an old Android application of mine, and I saw one thing I did to the effect of this:

        boolean emptyArray = true;
        for (int i = 0; i < array.size(); i++)
        {
            if (array.get(i) != null)
            {
                    emptyArray = false;
                    break;
            }
        }
        if (emptyArray == true)
        {
            return true;
        }
        return false;

There has to be a more efficient way of doing this -- but what is it?

emptyArray is defined as an ArrayList of Integers, which are inserted with a random number of null values (And later in the code, actual integer values).

Thanks!

Answer 1

Well, you could use a lot less code for starters:

public boolean isAllNulls(Iterable<?> array) {
    for (Object element : array)
        if (element != null) return false;
    return true;
}

With this code, you can pass in a much wider variety of collections too.

---

Java 8 update:

public static boolean isAllNulls(Iterable<?> array) {
    return StreamSupport.stream(array.spliterator(), true).allMatch(o -> o == null);
}

Answer 2

It's not detection of contains only null values but it maybe be enough to use just contains(null) method on your list.

Answer 3

There is no more efficient way. The only thing is you can do, is write it in more elegant way:

List<Something> l;

boolean nonNullElemExist= false;
for (Something s: l) {
  if (s != null) {
     nonNullElemExist = true;
     break;
  }
}

// use of nonNullElemExist;

Actually, it is possible that this is more efficient, since it uses Iterator and the Hotspot compiler has more info to optimize instead using size() and get().