JNI ERROR : attempt to pass an instance of java.lang.String as argument

Question

This is my some Java Code:

public class MainTest{

/*
...
*/

    public native void invokeByCPlusPlus();

    private void appendLine(String... strs){
        for(String str : strs) {
            System.out.println("get s : " + str);
        }
    }
}

and I want to use jni call my Java method "appendLine(String... strs)" when I call invokeByCPlusPlus() method in Java:

extern "C" void
Java_com_hengye_jnitest_MainTest_invokeByCPlusPlus(JNIEnv *env, jobject instance) {

    jclass clazz = env->GetObjectClass(instance);
    jmethodID methodId = env->GetMethodID(clazz, "appendLine", "([Ljava/lang/String;)V");

    jvalue values[2];
    jvalue *val1 = new jvalue();
    val1->l = env->NewStringUTF("invoke by C++ 1");
    values[0] = *val1;

    jvalue *val2 = new jvalue();
    val2->l = env->NewStringUTF("invoke by C++ 2");
    values[1] = *val2;

    env->CallVoidMethodA(instance, methodId, values);
    return;
}

then I get an error : JNI ERROR : attempt to pass an instance of java.lang.String as argument 1 to void com.hengye.ndktest.MainTest.appendLine(java.lang.String[])

only I declare appendLine method like this the code run normally:

private void appendLine(String str1, String str2){

   System.out.print(str1 + str2);

}

How can I solve this problem?

timrau · Accepted Answer · 2016-12-11 06:46:59Z

1

You cannot use jvalue[]. You need to use jobjectArray.

jobjectArray values = env->NewObjectArray(2, clazz, env->NewStringUTF(""));
env->SetObjectArrayElement(values, 0, env->NewStringUTF("invoke by C++ 1"));
env->SetObjectArrayElement(values, 1, env->NewStringUTF("invoke by C++ 2"));
env->CallVoidMethod(instance, methodId, values);

Note that I call CallVoidMethod instead of CallVoidMethodA.

answered Dec 11, 2016 at 6:46

timrau

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1 Comment

Jayden Yu Over a year ago

Thank you very much, but it works after change some code:

jclass stringClass = env->FindClass("java/lang/String");      jobjectArray values = env->NewObjectArray(3, stringClass, env->NewStringUTF(""));

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