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Easy Learn Java: Programming Articles, Examples and Tips - Page 385


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Ergonomics in the 5.0 Java Virtual Machine

Go to all tips in Java Installation, tunning, options...

Getting the best performance out of the JVM has often required detailed hand tuning of command line options. Yet many users never set command line options for performance. In order to give the best possible performance in a variety of situations Sun Microsystems has improved the performance of the JVM even when no command line options are used.

In J2SE 5.0 the default selection for the garbage collector, heap size, and runtime compiler are now chosen automatically. These new selections better match the needs of different types of applications while requiring less command line tuning.

In addition a different way of tuning the heap has been added for the throughput garbage collector. This new tuning allows the user to specify performance and memory utilization criteria to dynamically tune the sizes of the heap. This "self tuning" behavior is referred to in this document as "ergonomics". For more on ergonomics please see the Ergonomics in the 5.0 Java Virtual Machine document.

The performance improvements from ergonomics are significant. Here we compare SPECjbb2000 performance between J2SE 1.4.2 and J2SE 5.0.

Actual graphs and full article please read here



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Posted by jalex on Tuesday, July 19, 2005 (00:00:00) (3034 reads)

Is it possible to measure time in nanoseconds?

Go to all tips in Good To Know
Use public static long nanoTime(), since 1.5
Returns the current value of the most precise available system timer, in nanoseconds.

This method can only be used to measure elapsed time and is not related to any other notion of system or wall-clock time. The value returned represents nanoseconds since some fixed but arbitrary time (perhaps in the future, so values may be negative). This method provides nanosecond precision, but not necessarily nanosecond accuracy. No guarantees are made about how frequently values change. Differences in successive calls that span greater than approximately 292 years (263 nanoseconds) will not accurately compute elapsed time due to numerical overflow.

For example, to measure how long some code takes to execute:

   long startTime = System.nanoTime();
   // ... the code being measured ...
   long estimatedTime = System.nanoTime() - startTime;
 

Returns:
The current value of the system timer, in nanoseconds.

The method System.nanoTime() has been added, providing access to a nanosecond-granularity time source for relative time measurements. The actual precision of the time values returned by System.nanoTime() is platform-dependent.



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Posted by jalex on Monday, July 18, 2005 (00:00:00) (11573 reads)

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