Code to detect loops in linked lists in O(n)

LinkedListLoopDetector.java

public static boolean containsLoop(LinkedListNode list) {
  LinkedListNode slowIterator = list, fastIterator = list;
  // If a loop exists in the list, both iterators will be going round
  // and round in the loop, and at some point, they will be equal
  while (slowIterator != null && fastIterator != null) {
    slowIterator = slowIterator.getNext();
    try {
      fastIterator = fastIterator.getNext().getNext();
    } catch (NullPointerException npe) {
      fastIterator = null;
    }
    if (slowIterator == fastIterator)
      return true;
  }
  return false;
}