Iterator `next` method should throw `NoSuchElementException`JAVA-W0146

This class implements the java.util.Iterator interface. However, its next() method is not capable of throwing java.util.NoSuchElementException.

This is a violation of the Iterator interface's contract, and will not work with code that expects next() to throw when the iterator is exhausted.

The next() method should be changed so it throws NoSuchElementException if is called when there are no more elements to return.

Bad Practice

This is a nonconforming implementation and may mislead API consumers.

// Within iterator implementation
@Override
public T next() {
    if (hasNext()) { ... }
    else return null;
}

Recommended

This implementation should be preferred:

@Override
public T next() {
    if (hasNext()) { ... }
    else throw NoSuchElementException();
}

If the iterator will never throw, it may be preferable to write hasNext() to always return true, while throwing if hasNext() returns false. Obviously that would never occur, but it can serve to convey the intent. Always document such behavior for consumers of your API.

@Override
public boolean hasNext() {
    return true;
}

Otherwise, a NoSuchElementException must be thrown to ensure conformance with the Iterator API.

References

• SpotBugs - IT_NO_SUCH_ELEMENT