jvm.dll vs java.dll

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Naresh Agarwal - 14 Jun 2005 16:32 GMT

Hi

JDK 1.4 provides jvm.dll and java.dll libraries on windows and
libjvm.so and libjava.so on unix platforms (linux etc.)

What is difference between 'jvm' and 'java' libraries? I found that
java.dll is dependent on jvm.dll

In order to use JNI Invocation API (creating JVM etc.), which library
should be used?

thanks & regards,
Naresh

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Roland - 14 Jun 2005 17:46 GMT

> Hi
>
[quoted text clipped - 9 lines]
> thanks & regards,
> Naresh

"jvm.dll" is the Virtual Machine that interprets bytecodes and compiles
to native code when necessary (hotspots).
"jvm.dll" also contains the JNI_CreateJavaVM entry point, so this is the
one you need for JNI.

java.dll contains the code of several native methods in the Java API,
Object.getClass() for example.

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Roland de Ruiter
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Naresh Agarwal - 15 Jun 2005 12:14 GMT

thanks for reply.

I found that jvm.dll does not depend upon java.dll. So if jvm.dll is
the entry point, how java.dll is loaded. Is it loaded dynamically?

thanks,
Naresh

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Roland - 15 Jun 2005 12:43 GMT

> thanks for reply.
>
[quoted text clipped - 3 lines]
> thanks,
> Naresh

Guess so. java.dll also contains the native code for loading, finding
and defining Java classes (from .class files), quite important for
accessing Java's system classes and classes you compiled yourself. I
think java.dll gets loaded during the startup of the JVM.

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Roland de Ruiter
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Gordon Beaton - 15 Jun 2005 13:06 GMT

> I found that jvm.dll does not depend upon java.dll. So if jvm.dll is
> the entry point, how java.dll is loaded. Is it loaded dynamically?

On Linux, libjava.so depends on libjvm.so, but the converse is not
true:

$ readelf -d libjava.so
Dynamic segment at offset 0x208a8 contains 25 entries:
Tag Type Name/Value
0x00000001 (NEEDED) Shared library: [libjvm.so]
[...]

When the library contains such information, ld.so will load libjvm.so
automatically when a process loads libjava.so.

/gordon

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jvm.dll vs java.dll

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