Is there any reason to avoid the sentinel pattern in Java?

Question

I've heard people advise that one should always use the Iterator pattern to control loops rather than throwing an exception (which is how it's done in Python iterators) or using the Sentinel pattern, whereby a special, sentinel value (often null) is returned to indicate the end of the iteration.

Does best practice advise against the sentinel pattern? If so, why? (other than it not working with the foreach syntax in Java 1.5).

Edit: Code example 1 - Sentinel Pattern

Reader r = ...;
for( int val = r.read(); val != -1; val = r.read()) {
   doSomethingWith(val);
}

Code example 2 - Iterator Pattern

for(Iterator<Thing> it = getAnIterator() ; it.hasNext(); ) {
  Thing t = it.next();
  doSomethingWith(t);
}

Answer 1

The issue with the Sentinel pattern is that it explicitly excludes the sentinel value from the set of values that are valid elements. I.e., if you have a list of objects which can validly contain null as an element, using null as a sentinel value is a fail.

Answer 2

Exceptions should only be used in "exceptional" situations. Concluding or breaking out of a loop is normal program flow, not an exceptional situation.

Additionally, when working in Java, (or any language for that matter), you want to use patterns and conventions that are common and well known in the community because other Java programmers may need to maintain your code. If they do, they will most likely expect to see Iterators, not the sentinel pattern.