Calling JAVA from RPG ( passing string variable )

I'm trying to call my java methods from RPG, everything works but passing
string variables. 
Probably I have some issues with data conversion. 
Error I'm getting is : 
Message . . . . : Java exception received when calling Java method (C G D 
F). 
Cause . . . . . : RPG procedure TEST in program ROMAN/TEST received Java 
exception "java.lang.NoSuchMethodError: testStuff" when calling method 
"testStuff" with signature "([B)I" in class "MyClass". 
But prototype of the java function is correct : 
Compiled from MyClass.java 
public class MyClass extends java.lang.Object 
public MyClass(); 
/* ()V */ 
public static int testStuff(byte[]); 
/* ([B)I */ 
Here is my java class : 
public class MyClass {

public static int testStuff( byte[] test ){
int size =0;
size = test.length;
return size; 
} 
} 
Here is the Prototype : 
D testStuff PR 10i 0 ExtProc(*JAVA:
D 'MyClass':
D 'testStuff')
D Static
D teststr 30A 
And here is the RPG programm :
H DftActGrp(*NO) ActGrp(*CALLER)
/Copy *LibL/RPGSRC,TEST1PR
D first S 10i 0 Inz(23)
D second S 10i 0 Inz(18)
D sum S 10i 0
D testStr S 30A
/Free
// call my home grown method
testStr = 'roman';
sum = testStuff(testStr);
Dsply testStr;
/End-Free 
Thanks, 
Roman 
www.aadt.com