Classy Puzzlers - Java Puzzlers: Traps, Pitfalls, and Corner Cases - page 157

}
Note, however, that the program is not using the local variable creature . Therefore, it makes more
sense to replace the declaration with a naked constructor invocation, emphasizing that the reference
to the newly created object is being discarded:
for (int i = 0; i < 100; i++)
new Creature();
If either of these changes is made, the program will print 100 as expected.
Note that the variable used to keep track of the number of Creature instances ( numCreated ) is a
long rather than an int . It is quite conceivable that a program might create more instances of some
class than the maximum int value but not the maximum long value. The maximum int value is
2 31 - 1, or about 2.1 x 10 9 ; the maximum long value is 2 63 - 1, or about 9.2 x 10 18 . Today, it is
possible to create about 10 8 objects per second, which means that a program would have to run
about three thousand years before a long object counter would overflow. Even in the face of
increasing hardware speeds, long object counters should be adequate for the foreseeable future.
Also note that the creation counting strategy in this puzzle is not thread-safe. If multiple threads can
create objects in parallel, the code to increment the counter and the code to read it must be
synchronized:
// Thread-safe creation counter
class Creature {
private static long numCreated;
public Creature() {
synchronized (Creature.class) {
numCreated++;
}
}