QAndroidJniObject string = QAndroidJniObject::callStaticObjectMethod<jstring>("com/your/project/YourClass", "helloWorld");
Is equivalent to:
QAndroidJniObject string = QAndroidJniObject::callStaticObjectMethod("com/your/project/YourClass", "helloWorld", "()Ljava/lang/String;");
For trivial signatures, that is, signatures that takes no arguments and returns one of the know jni types, you can write the short version by supplying the template type.