This section describes some of the methods inSystem
that aren't covered in the previous sections.The
arrayCopy
method efficiently copies data between arrays. For more information, refer to Arrays in the Language Basics lesson.The
currentTimeMillis
andnanoTime
methods are useful for measuring time intervals during execution of an application. To measure a time interval in milliseconds, invokecurrentTimeMillis
twice, at the beginning and end of the interval, and subtract the first value returned from the second. Similarly, invokingnanoTime
twice measures an interval in nanoseconds.
NOTE: The accuracy of bothcurrentTimeMillis
andnanoTime
is limited by the time services provided by the operating system. Do not assume thatcurrentTimeMillis
is accurate to the nearest millisecond or thatnanoTime
is accurate to the nearest nanosecond. Also, neithercurrentTimeMillis
nornanoTime
should be used to determine the current time. Use a high-level method, such asjava.util.Calendar.getInstance
.The
exit
method causes the Java virtual machine to shut down, with an integer exit status specified by the argument. The exit status is available to the process that launched the application. By convention, an exit status of0
indicates normal termination of the application, while any other value is an error code.