Effective Java

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ITEM 58: PREFER FOR-EACH LOOPS TO TRADITIONAL FOR LOOPS
265
// Can you spot the bug?
enum Suit { CLUB, DIAMOND, HEART, SPADE }
enum Rank { ACE, DEUCE, THREE, FOUR, FIVE, SIX, SEVEN, EIGHT,
NINE, TEN, JACK, QUEEN, KING }
...
static Collection suits = Arrays.asList(Suit.values());
static Collection ranks = Arrays.asList(Rank.values());
List deck = new ArrayList<>();
for (Iterator i = suits.iterator(); i.hasNext(); )
for (Iterator j = ranks.iterator(); j.hasNext(); )
deck.add(new Card(i.next(), j.next()));
Don’t feel bad if you didn’t spot the bug. Many expert programmers have
made this mistake at one time or another. The problem is that the 
next
method is
called too many times on the iterator for the outer collection (
suits
). It should be
called from the outer loop so that it is called once per suit, but instead it is called
from the inner loop, so it is called once per card. After you run out of suits, the
loop throws a 
NoSuchElementException
.
If you’re really unlucky and the size of the outer collection is a multiple of the
size of the inner collection—perhaps because they’re the same collection—the
loop will terminate normally, but it won’t do what you want. For example,
consider this ill-conceived attempt to print all the possible rolls of a pair of dice: