java: how many times is the collection expression evaluated in a “foreach”

Question

if I do this in Java:

for(String s : myCollection.expensiveListGeneration())
{
      doSomething();
}

is expensiveListGeneration() invoked

Answer 1

It's invoked once, and not implementation dependant. The for-each loop is based on the Iterable interface. All it does is call the collection's iterator() method once at the beginning, and then works with that iterator.