Any null safe alternative to ArrayList.addAll?

Question

I was refactoring some old code of mine that I\'ve written and I stumbeled on this code:

    List fullImagePool = new ArrayList<>();
           


        

Answer 1

Just write a small utility method:

public static <E> void addAllIfNotNull(List<E> list, Collection<? extends E> c) {
    if (c != null) {
        list.addAll(c);
    }
}

so that you can write:

List<OcmImageData> fullImagePool = new ArrayList<>();
addAllIfNotNull(fullImagePool, style.getTestMH());
addAllIfNotNull(fullImagePool, style.getTrousers());
addAllIfNotNull(fullImagePool, style.getDetailRevers());
// ...etc

Answer 2

In Java 8 Use below code:-

Optional.ofNullable(listToBeAdded).ifPresent(listToBeAddedTo::addAll)

listToBeAdded - The list whose elements are to be added. listToBeAddedTo - The list to which you are adding elements using addAll.

Answer 3

This refactors cleanly to

for (OcmImageData elem : new List<OcmImageData>[] { style.getTestMH(), style.getTrousers() /* etc */}) {
    if (CollectionUtils.isNotEmpty(elem)) {
        fullImagePull.addAll(elem);
    }
}

To answer your original question, no, you will have to do your own null check. You can see Guava's methods will throw an NPE, and Apache's methods explicitly require the input to be not null.

Answer 4

Using Java 8:

List<OcmImageData> fullImagePool = Stream.of(style.getTestMH(), /* etc */)
                                         .filter(Objects::nonNull)
                                         .flatMap(l -> l.stream())
                                         .collect(Collectors.toList());