MethodHandles and class initialization

[John Rose]

On Jul 19, 2012, at 7:04 PM, Dain Sundstrom wrote:

> I have some code that tries to get the value of a static final field using a MethodHandle, and I find that the field is null because the class isn't initialized. Is calling a method handle supposed to cause a class to initialize (run the <clinit> method)?

Yes, the behavior of findStaticGetter is based on the getstatic bytecode, which includes (as you expected) the initialization barrier.  Same point for putstatic and invokestatic, and REF_newInvokeSpecial (combination of new + <init>).

The JDK 7 implementation has bugs regarding some of these guys.  The upcoming integration of "lazy method handles" includes complete coverage for these initialization paths.

> In a related question, what is the best way to force initialization and when do you do the initialization? in the bootstrap method?

The best way to force initialization of a class is to fetch a static field or call a static method.  You can do this with reflection, or (if the above bugs are fixed) via method handles.  You can also allocate an instance of the class.

— John
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