Check two arguments for null in an elegant way

Question

I am iterating over two collections and check if both collections contain the same elements. I can't use Java 8.

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edit 1 year after:

I created the method in the question to check if two Collections contain the same elements, without thinking about the fact that I am passing two Collection implementations into the method.

But Collection does not determine how elements are sorted. And I am iterating over the collections. Thus, some implementation of Collection could save elements in random order, while containing the same elements.

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Both collections contain elements that are comparable and the content is defined as equal, if all elements return a x.compareTo(y) with 0.

Two values are defined as different, if one of them is null, but not the other. I want to find an elegant way to compare on nullity and prevent a null check on the final compareTo().

My current implementation:

    public static <T extends Comparable<T>> boolean isSame(@Nullable Collection<T> a, @Nullable Collection<T> b) {

    if (a == null || b == null) {
        return (a == null && b == null);
    }

    if (a.size() != b.size()) {
        return false;
    }
    Iterator<T> aIt = a.iterator();
    Iterator<T> bIt = b.iterator();
    while (aIt.hasNext()) {
        T aValue = aIt.next();
        T bValue = bIt.next();
        if (aValue == null || bValue == null) {
            if (aValue == null ^ bValue == null) {
                return false;
            }
            //both null, don't compare, continue looping...
        } else if (aValue.compareTo(bValue) != 0) {
            return false;
        }
    }
    return true;
}

I want to continue the while loop, if both values are null, because that is defined as equal.

But I am struggling with this part:

if (aValue == null || bValue == null) {
        if (aValue == null ^ bValue == null) {
            return false;
        }
}

Question:

Is there a more elegant and readable way to compare on nullity, do a further compare if both are not null, return false if only one is null, and continue the loop, if both values are null?

Answer 1

The sequence as follows should work well:

if(aValue == null && bValue == null) continue; // both null; continue
if(aValue == null || bValue == null) return false; // any null; return false
if(aValue.compareTo(bValue) != 0) { // both non-null; compare
    return false;
}