Calling ``++Iterator.hasNext()++`` is not supposed to have any side effects, and therefore should not change the state of the iterator. ``++Iterator.next()++`` advances the iterator by one item. So calling it inside ``++Iterator.hasNext()++``, breaks the ``++hasNext()++`` contract, and will lead to unexpected behavior in production.

== Noncompliant Code Example

----
public class FibonacciIterator implements Iterator<Integer>{
...
@Override
public boolean hasNext() {
  if(next() != null) {
    return true;
  }
  return false;
}
...
}
----