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Essential Classes
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The Platform Environment
Miscellaneous Methods in System
This section describes some of the methods in
System 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
and
nanoTime
methods are useful for measuring time intervals during execution of an
application. To measure a time interval in milliseconds, invoke
currentTimeMillis twice, at the beginning and end of the
interval, and subtract the first value returned from the second.
Similarly, invoking nanoTime twice measures an interval
in nanoseconds.
NOTE: The accuracy of both
currentTimeMillis and
nanoTime is limited by the time services provided by the
operating system. Do not assume that
currentTimeMillis is accurate to the nearest millisecond
or that
nanoTime is accurate to the nearest nanosecond.
Also, neither
currentTimeMillis nor
nanoTime
should be used to determine the current time. Use a high-level
method, such as
java.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 of
0 indicates normal termination of the application, while
any other value is an error code.
