Call methods of a class generated in runtime

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jcall fails with NoSuchMethodError when calling methods of a dynamically compiled class.

I use InMemoryJavaCompiler to compile a new class and create its instance. (InMemoryJavaCompiler is based on javax.tools.*, so quite standard approach).

const JInMemoryJavaCompiler = @jimport org.mdkt.compiler.InMemoryJavaCompiler

function mkclass(name::String, src::String)
    jcompiler = jcall(JInMemoryJavaCompiler, "newInstance", JInMemoryJavaCompiler, ())
    return jcall(jcompiler, "compile", JClass, (JString, JString), name, src)
end

function instantiate(name::String, src::String)
    jclass = mkclass(name, src)
    return jcall(jclass, "newInstance", JObject, ())
end


init()
name = "julia.compiled.Hello"
src = """
        package julia.compiled;

        public class Hello {

            public String hello(String name) {
                return "Hello, " + name;
            }

            public void goodbye() {
                System.out.println("Goodbye!");
            }
        }
    """

obj = instantiate(name, src)

The resulting object looks like the ordinary one and I can see the methods I defined:

julia> listmethods(obj)
11-element Vector{JMethod}:
 java.lang.String hello(java.lang.String)
 void goodbye()
 void wait(long)
 void wait(long, int)
 void wait()
 boolean equals(java.lang.Object)
 java.lang.String toString()
 int hashCode()
 java.lang.Class getClass()
 void notify()
 void notifyAll()

However, calling them with jcall fails, even though calling the inherited methods works fine:

julia> jcall(obj, "hello", JString, (JString,), "Bob")
Exception in thread "main" java.lang.NoSuchMethodError: hello
ERROR: JavaCall.JavaCallError("Error calling Java: java.lang.NoSuchMethodError: hello")
Stacktrace:
 [1] geterror(allow::Bool)
   @ JavaCall ~/.julia/packages/JavaCall/MlduK/src/core.jl:418
 [2] jcall(obj::JObject, method::String, rettype::Type, argtypes::Tuple{DataType}, args::String)
   @ JavaCall ~/.julia/packages/JavaCall/MlduK/src/core.jl:244
 [3] top-level scope
   @ REPL[13]:1

julia> jcall(obj, "goodbye", Nothing, ())
Exception in thread "main" java.lang.NoSuchMethodError: goodbye
ERROR: JavaCall.JavaCallError("Error calling Java: java.lang.NoSuchMethodError: goodbye")
Stacktrace:
 [1] geterror(allow::Bool)
   @ JavaCall ~/.julia/packages/JavaCall/MlduK/src/core.jl:418
 [2] jcall(::JObject, ::String, ::Type, ::Tuple{})
   @ JavaCall ~/.julia/packages/JavaCall/MlduK/src/core.jl:244
 [3] top-level scope
   @ REPL[14]:1

julia> jcall(obj, "equals", jboolean, (JObject,), obj)
0x01

What's even more confusing, these new methods can actually be called using the reflection:

function jcall2(jobj::JavaObject, name::String, ret_type, arg_types, args...)
    jclass = getclass(jobj)
    jargs = [a for a in convert.(arg_types, args)]  # convert to Vector
    meth = jcall(jclass, "getMethod", JMethod, (JString, Vector{JClass}), name, getclass.(jargs))
    return meth(jobj, jargs...)
end

julia> jcall2(obj, "hello", JString, (JString,), "Bob")
"Hello, Bob"

julia> jcall2(obj, "goodbye", Nothing, ())
Goodbye!

Although it fails with NoSuchMethodException for the inherited method ¯_(ツ)_/¯:

julia> jcall2(obj, "equals", jboolean, (JObject,), obj)
Exception in thread "main" java.lang.NoSuchMethodException: julia.compiled.Hello.equals(julia.compiled.Hello)
        at java.base/java.lang.Class.getMethod(Class.java:2108)
ERROR: JavaCall.JavaCallError("Error calling Java: java.lang.NoSuchMethodException: julia.compiled.Hello.equals(julia.compiled.Hello)")
Stacktrace:
 [1] geterror(allow::Bool)
   @ JavaCall ~/.julia/packages/JavaCall/MlduK/src/core.jl:418
 [2] geterror
   @ ~/.julia/packages/JavaCall/MlduK/src/core.jl:403 [inlined]
 [3] _jcall(::JClass, ::Ptr{Nothing}, ::Ptr{Nothing}, ::Type, ::Tuple{DataType, DataType}, ::String, ::Vararg{Any})
   @ JavaCall ~/.julia/packages/JavaCall/MlduK/src/core.jl:373
 [4] jcall(::JClass, ::String, ::Type, ::Tuple{DataType, DataType}, ::String, ::Vararg{Any})
   @ JavaCall ~/.julia/packages/JavaCall/MlduK/src/core.jl:245
 [5] jcall2(jobj::JObject, name::String, ret_type::Type, arg_types::Tuple{DataType}, args::JObject)
   @ Main ./REPL[17]:4
 [6] top-level scope
   @ REPL[18]:1

The code above is executable from the Spark#new-api branch, but honestly I hope that I'm just doing some stupid mistake that a keen eye can catch just from the description.

Reproduce the failure with the InMemoryJavaCompiler example from the issue, then start in JavaCall's core.jl around jcall and the reported lines 244 and 373. Compare ordinary dispatch with the reflection-based jcall2 path; done means methods on dynamically compiled classes can be called through jcall while inherited methods continue to work.

Written by the indexing model from the issue text.

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