Miscellaneous Methods in System
This section describes some of the methods in
System that aren't covered in the previous sections.
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.
The accuracy of both
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
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.