Android java传递int类型数据给C

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity" >

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="click"
        android:text="传递int类型参数" />

</LinearLayout>

package com.wuyudong.javapassdata;

public class JNI {
    //传递两个int类型的变量给C，让C加一下返回
    static{
        System.loadLibrary("passdata");
    }
    public native int add(int x, int y);
    public native String sayHelloInC(String s);
    public native int[] arrElementsIncrease(int[] intArray);

}

#include <jni.h>

/*
 * Class:     com_wuyudong_javapassdata_JNI
 * Method:    add
 * Signature: (II)I
 */
JNIEXPORT jint JNICALL Java_com_wuyudong_javapassdata_JNI_add(JNIEnv * env,
        jobject clazz, jint x, jint y) {
    return x + y;
}

package com.wuyudong.javapassdata;

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.View;
import android.widget.Toast;

public class MainActivity extends Activity {

    public JNI jni;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        jni = new JNI();
    }

    public void click(View v) {
        Toast.makeText(getApplicationContext(), jni.add(3, 4)+"", 0).show();
    }

}