http://java.sun.com/j2se/1.4.2/docs/api/java/lang/System.html#currentTimeMillis() says:

Returns the current time in milliseconds. Note that while the unit of time of the return value is a millisecond, the granularity of the value depends on the underlying operating system and may be larger. For example, many operating systems measure time in units of tens of milliseconds.

It is not clear to me if I am guaranteed that this code will always print ever increasing (or the same) numbers.

while (1) { 
    System.out.println(System.currentTimeMillis() );
}