Which classes need to be supplied by any JVM?

[David Holmes - Sun Microsystems]

Stephen,

Stephen Colebourne said the following on 08/21/09 18:14:
> If you wanted to code from scratch a JVM, but not include the rest of 
> the Java SE platform (such as the .class files), what would you need to 
> include? Is Object.class mandatory for a pure JVM? Anything else?
> 
> The answers given imply that the JVM is not an isolated well defined 
> component. Yet that argues against being able to write a new programming 
> language for the JVM that has no integration whatsoever with the Java 
> language and just emits 'pure bytecode' for a 'pure JVM'.

I think you would need to separate the bytecode-engine part of the JVM 
from the "Java runtime platform" part. The bytecode engine has few 
dependencies on classes, perhaps not even Object, while the runtime 
environment has many dependencies.

David Holmes

> I, like Carsten, find it odd if this isn't well-defined.
> 
> Stephen
> 
> David Holmes - Sun Microsystems wrote:
>> As Martin stated what you are looking for is not part of the JVMS nor 
>> the JLS, but the platform specification, which is essentially the 
>> entire set of Java API's as found for example here:
>>
>> http://java.sun.com/javase/6/docs/index.html
>>
>> But the implementation of those classes will then have dependencies on 
>> other implementation specific classes, so I'm not sure that you will 
>> be able to establish a transitive closure of required classes that is 
>> independent of the JVM in question.
>>
>> If you were thinking about this from a basic language perspective - eg 
>> we must have Object, and we must have Class, and array implies 
>> Serializable etc, then there is a core set of classes that form the 
>> transitive closure of the JVM bootstrap process. If you are interested 
>> in that then -XX:+TraceClassLoading (might need a debug VM) will give 
>> you the set used by a particular VM. But again this list is dependent 
>> on how those classes are implemented themselves, so the list is JVM 
>> dependent.
>>
>> HTH
>>
>> David Holmes
>>
>> Martin Buchholz said the following on 08/21/09 03:32:
>>> The set of all public APIs that must be part of the java se platform
>>> are tested by the platform tck, in particular by the "signature test",
>>> and you can get the sources for that test (for research only)
>>> and from that it should be possible (with work) to get a list of
>>> all required classes.  But that's a very large list, so is probably not
>>> what you want.  In practice, the subset of rt.jar of public classes
>>> matching java.* or javax.* is a pretty good approximation.
>>>
>>> Martin
>>>
>>> On Thu, Aug 20, 2009 at 08:26, Carsten Otto 
>>> <otto at informatik.rwth-aachen.de 
>>> <mailto:otto at informatik.rwth-aachen.de>> wrote:
>>>
>>>     Hello,
>>>
>>>     I am working on automated termination analysis of Java Bytecode 
>>> and I am
>>>     missing an important bit of information in the Java Virtual Machine
>>>     Specification (JVMS). I'd be happy to get some help from you!
>>>
>>>     Every JVM needs to provide certain classes including code for their
>>>     native
>>>     methods, e.g. java.lang.Object (obvious) and java.io.Serializable
>>>     (because
>>>     every array implements it). The list of such classes can easily be
>>>     extended, but I have huge problems finding a lower bound to keep
>>>     this list
>>>     as small[1] as allowed according to the JVMS.
>>>
>>>     Is there some part of the specification that states which classes
>>>     need to
>>>     be provided? I can only see references to the API (e.g. "reflective
>>>     APIs"),
>>>     but no clear definition of the classes that need to exist. In the
>>>     current
>>>     draft for JVMS 3rd edition, the necessity to include
>>>     java.io.Serializable
>>>     is not even part of the JVMS, this is only visible by looking at the
>>>     definition of arrays in the Java Language Specification (JLS).
>>>
>>>     Some hints in this direction are also appreciated. So far I can only
>>>     guess,
>>>     that sun.awt.* is not part of the language defined in the JVMS - 
>>> but who
>>>     knows?
>>>
>>>     [1]: Sadly, just using whatever Sun or OpenJDK provide in rt.jar
>>>     does not
>>>     work.
>>>
>>>     Thanks a lot,
>>>     --
>>>     Carsten Otto           otto at informatik.rwth-aachen.de
>>>     <mailto:otto at informatik.rwth-aachen.de>
>>>     LuFG Informatik 2      http://verify.rwth-aachen.de/otto/
>>>     RWTH Aachen            phone: +49 241 80-21211
>>>
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>>>
>>