How to call a static method of java from c++ side?

[stereomatching]

simpleJNI.hpp

@#include <QObject>

class simpleJNI : public QObject
{
Q_OBJECT
public:
explicit simpleJNI(QObject *parent = nullptr);

Q_INVOKABLE QString printHelloWorld();

};@

simpleJNI.cpp

@
#include "simpleJNI.hpp"

#include <QDebug>
#include <QtAndroidExtras/QAndroidJniObject>

simpleJNI::simpleJNI(QObject *parent) :
QObject(parent)
{
}

QString simpleJNI::printHelloWorld()
{
QAndroidJniObject str = QAndroidJniObject::callStaticObjectMethod("adv/appBucksAdv",
"getString",
"(V)Ljava/lang/String;"
);

return str.toString();

}
@

appBucksAdv.java
@package adv;

import org.qtproject.qt5.android.bindings.QtApplication;
import org.qtproject.qt5.android.bindings.QtActivity;
import android.content.Context;

public class appBucksAdv extends QtActivity
{
public static String getString()
{
return "hello world";
}
}
@

main.qml

@
import QtQuick 2.2
import QtQuick.Controls 1.1

Rectangle {
width: 100
height: 62

color: "red"

Text{
    id: text
    height: 30
    width: parent.width
    anchors.centerIn: parent
}

MouseArea{
    anchors.fill: parent

    onClicked: {
        text.text = text.text + simpleJNI.printHelloWorld() + "\n"
    }
}

}
@

But the program do not print "helloWorld\n"

message :
W/dalvikvm( 6727): Bogus method descriptor: (V)Ljava/lang/String;

"Layout of the projects":https://github.com/stereomatchingkiss/blogCodes2/tree/master/androidTest

[stereomatching]

If I change the signature of the function to

@public static String printHelloWorld(int a)
{
return "hello world";
}@

and simpleJNI.cpp to

@QString simpleJNI::printHelloWorld()
{
QAndroidJniObject str = QAndroidJniObject::callStaticObjectMethod("adv/appBucksAdv",
"printHelloWorld",
//change (V) to (I)
"(I)Ljava/lang/String;",
23);

return str.toString();

}
@

The codes work

[mobi]

try "()Ljava/lang/String;" or

@QString simpleJNI::printHelloWorld()
{
QAndroidJniObject str = QAndroidJniObject::callStaticObjectMethod<jstring>("adv/appBucksAdv",
"printHelloWorld");

return str.toString();

}@