Question

Since a static function call is translated into a static invocation bytecode regardless of how the definition exists… is there some way to force a caller of a static function to compile successfully even when the target function and class don’t exist yet?

I want to be able to compile calls to functions that don’t exist yet. I need to tell the compiler to trust me that at runtime, I’ll have them properly defined and in the classpath so go ahead and compile it for now.

Is there a way to do this?

Answer 1

Reflectively yes, but not via a regular call.

The call requires an entry in the string pool that includes the method name and parameter types so the compiler needs to be able to decide on a signature for the method.

invokestatic <method-spec>

<method-spec> is a method specification. It is a single token made up of three parts: a classname, a methodname and a descriptor. e.g.

 java/lang/System/exit(I)V

is the method called “exit” in the class called “java.lang.System”, and it has the descriptor “(I)V” (i.e. it takes an integer argument and returns no result).

Consider

AClass.aStaticMethod(42)

Without knowing anything about AClass, it could be a call to any of

1. AClass.aStaticMethod(int)
2. AClass.aStaticMethod(int...)
3. AClass.aStaticMethod(long)
4. AClass.aStaticMethod(long...)
5. ditto for float and double
6. AClass.aStaticMethod(Integer)
7. AClass.aStaticMethod(Number)
8. AClass.aStaticMethod(Comparable<? extends Integer>)
9. AClass.aStaticMethod(Object)
10. AClass.aStaticMethod(Serializable)

and probably a few others that I’ve missed.