Null check in an enhanced for loop

Question

What is the best way to guard against null in a for loop in Java?

This seems ugly :

if (someList != null) {
    for (Object object : someList) {
            


        

Answer 1

Use, CollectionUtils.isEmpty(Collection coll) method which is Null-safe check if the specified collection is empty.

for this import org.apache.commons.collections.CollectionUtils.

Maven dependency

<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-collections4</artifactId>
    <version>4.0</version>
</dependency>

Answer 2

You could potentially write a helper method which returned an empty sequence if you passed in null:

public static <T> Iterable<T> emptyIfNull(Iterable<T> iterable) {
    return iterable == null ? Collections.<T>emptyList() : iterable;
}

Then use:

for (Object object : emptyIfNull(someList)) {
}

I don't think I'd actually do that though - I'd usually use your second form. In particular, the "or throw ex" is important - if it really shouldn't be null, you should definitely throw an exception. You know that something has gone wrong, but you don't know the extent of the damage. Abort early.

Answer 3

for (Object object : someList) {

   // do whatever
}  throws the null pointer exception.

Answer 4

I have modified the above answer, so you don't need to cast from Object

public static <T> List<T> safeClient( List<T> other ) {
            return other == null ? Collections.EMPTY_LIST : other;
}

and then simply call the List by

for (MyOwnObject ownObject : safeClient(someList)) {
    // do whatever
}

Explaination: MyOwnObject: If List<Integer> then MyOwnObject will be Integer in this case.

Answer 5

With Java 8 Optional:

for (Object object : Optional.ofNullable(someList).orElse(Collections.emptyList())) {
    // do whatever
}