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Java Forum / General / June 2006

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Quick question about JIT

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Rhino - 06 Jun 2006 18:15 GMT
Given this as the output from java -version:

java version "1.4.1_02"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.1_02-b06)
Java HotSpot(TM) Client VM (build 1.4.1_02-b06, mixed mode)

Is this a JIT compiler? How do you know? In other words, what wording is the
giveaway that this is or isn't a JIT compiler? Or do I need a different
command or technique to determine that it is JIT?

Signature

Rhino

Thomas Hawtin - 06 Jun 2006 18:43 GMT
> Given this as the output from java -version:
>
[quoted text clipped - 5 lines]
> giveaway that this is or isn't a JIT compiler? Or do I need a different
> command or technique to determine that it is JIT?

HotSpot(TM) Client is the compiler in this case. JITs compile code on
first use. HotSpot is an adaptive compiler, and doesn't compile until
after the code has already run for a while.

You can switch the compiler off with -Xint, in which case the "mixed
mode" part of the message will change to "interpreted mode". -Xcomp will
turn off the compiler, giving "compiled mode".

There are much more recent versions of Java 1.4 than that, which should
have a number of security fixes present.

Tom Hawtin
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Unemployed English Java programmer
http://jroller.com/page/tackline/

Rhino - 06 Jun 2006 22:41 GMT
>> Given this as the output from java -version:
>>
[quoted text clipped - 16 lines]
> There are much more recent versions of Java 1.4 than that, which should
> have a number of security fixes present.

Thanks for the info, Thomas! I'm afraid I've never looked at the details of
Java compilers very closely :-)

--
Rhino
Chris Uppal - 06 Jun 2006 19:24 GMT
> In other words, what wording is
> the giveaway that this is or isn't a JIT compiler?

There isn't any; you just have to know.

There's usually information in the documentation which comes with the download
(not the JavaDoc), but quite often you have to know what the /previous/ version
was like to make sense of the changes they describe.  Also you may have to read
between the lines a little -- for instance if there's an option to disable the
JIT, then it's a fair guess that there is a JIT in use normally ;-)

But the bottom line is you have to consume all the available information, /and/
remember it.  A geek thing ;-)

Find your inner 13-y-o boy....

   -- chris
Rhino - 06 Jun 2006 22:41 GMT
>> In other words, what wording is
>> the giveaway that this is or isn't a JIT compiler?
[quoted text clipped - 16 lines]
>
> Find your inner 13-y-o boy....

I suspected it was one of those kinds of things but thought I'd asked in
case there was a more obvious way to determine whether the compiler was JIT.
Thanks, Chris!

--
Rhino


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