Unsigned char[] problem

Question

hi,
I am using JNI to test a C++ method that generates a random 128-byte unsigned char []. In my code, I've used a char[] to pass the unsigned char[] (as it always gives a positive number) and returned it as a jstring in Java.
However, I'm not sure in Java how I can catch the unsighed bytes using the String returned. I tried using int[] and float[] but somehow I still get negative bytes.
Could anyone pls give me some hints? any help would be greatly appreciated.
JNIEXPORT jstring JNICALL Java_RNGInvoker_getRNG(JNIEnv *env, jobject obj)
     RNG R;
     unsigned char Data[128];
     R.gen_num(Data);
     char Data2[128];
     for(int i=0;i<RNG::RNG_RANGE;i++) {
          Data2=Data[i];
     return (*env).NewStringUTF(Data2);
In Java,
class RNGInvoker {
    public native String getRNG();
    static {
        System.loadLibrary("rng");
    public static void main(String[] args) {
        String temp = new RNGInvoker().getRNG();
        byte aa[] = new byte[128];
        int bb[] = new int[128];
        aa = temp.getBytes();
        for(int i=0; i<128; i++) {
            bb[i] = Integer.parseInt(String.valueOf(aa));
System.out.println(aa[i] + ";" + bb[i]);

Answer 1

C/C++ uses 'bytes' for 'char'. Java uses 'chars' in Strings, not bytes. You are generating a byte array. You are then trying to return a byte array as a String. When java uses a byte array to create a String it maps it using the default language of the system. This might or might not lead to changes in actual values.
If you want to generate chars then figure out what the valid chars are for the range and language you are using.
If you want a byte array then return that not a String.