Fwd: An undefined behavior w.r.t. <clinit>

Yuting Chen chenyt.cs.sjtu at gmail.com
Sun Jul 12 17:02:30 UTC 2015

Hi, Gilles, thank you for your information. I read jvms again, and
indeed, it says

1. A class or interface has at most one class or interface
initialization method and is initialized (§5.5) by invoking that
method. The initialization method of a class or interface has the
special name <clinit>, takes no arguments, and is void (§4.3.3).

2. Other methods named <clinit> in a class file are of no consequence.
They are not class or interface initialization methods. They cannot be
invoked by any Java Virtual Machine instruction and are never invoked
by the Java Virtual Machine itself.

3. In a class file whose version number is 51.0 or above, the method
must additionally have its ACC_STATIC flag (§4.6) set in order to be
the class or interface initialization method.

4. This requirement was introduced in Java SE 7. In a class file whose
version number is 50.0 or below, a method named <clinit> that is void
and takes no arguments is considered the class or interface
initialization method regardless of the setting of its ACC_STATIC

Wait..., the sentence still reads a little strange, because the method
in my class is "public abstract void <clinit>();" and I still cannot
decide whether it should have any consequence or not, even though it
may not be an initialization method because it does not have an
ACC_STATIC flag. (it seems that the order of the paragraphs should be
changed to 1->3->4->2.)

In any case, the method has an invalid name (because it has a name
<clinit>) or invalid signature (because it does not have an ACC_STATIC
flag). I am afraid that it still should be rejected by HotSpot for
some format error.

For you question, if the class has a version number less than 51, a
format error will be thrown out when it is run on HotSpot and IBMJ9
("Exception in thread "main" java.lang.ClassFormatError: Absent Code
attribute in method that is not native or abstract in class file
M1436188543_V46"). The results are different only when the version
number is greater than 51.

The two classes are attached. Hope that you can get them.

Yuting Chen

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