How to return ArrayList<Boolean> in JNI java?-CodePudding

I'm new to JNI and I want to create an ArrayList<Boolean> from the C side.

I have the following situation:

import java.util.ArrayList;

public class createArrayJNI {
    static {
        System.loadLibrary("libnative");
    }
    
    public static void main(String[] args) {
        createArrayJNI jni =  new createArrayJNI();
        ArrayList<Boolean> array = jni.creatArray();
        System.err.println(array);
    }

    public native ArrayList<Boolean> creatArray();
}

and my cpp file is:

...
JNIEXPORT jobject JNICALL Java_createArrayJNI_creatArray
(JNIEnv \*env, jobject thisObject) {

    jclass java_util_class = env->FindClass("java/util/ArrayList");
        jmethodID java_util_method_constructor = env->GetMethodID(java_util_class, "<init>", "()V");
        jmethodID java_add_method = env->GetMethodID(java_util_class, "add", "(Ljava/lang/Object;)Z");
        jobject java_util_object = env->NewObject(java_util_class, java_util_method_constructor, "");
        jboolean a = true;
         env->CallBooleanMethod(java_util_object, java_add_method, a);
    
         return java_util_object;
}

It shows me:

# 
# A fatal error has been detected by the Java Runtime Environment:
# 
# SIGSEGV (0xb) at pc=0x00000001099110ac, pid=24207, tid=4355
# 
# JRE version: OpenJDK Runtime Environment Homebrew (19.0.1) (build 19.0.1)
# Java VM: OpenJDK 64-Bit Server VM Homebrew (19.0.1, mixed mode, sharing, tiered, compressed oops, compressed class ptrs, g1 gc, bsd-aarch64)
# Problematic frame:
# V  \[libjvm.dylib 0x1f10ac\]  AccessInternal::PostRuntimeDispatch\<G1BarrierSet::AccessBarrier\<598116ull, G1BarrierSet\>, (AccessInternal::BarrierType)2, 598116ull\>::oop_access_barrier(void\*) 0xc
# 
# No core dump will be written. Core dumps have been disabled. To enable core dumping, try "ulimit -c unlimited" before starting Java again
# 
# An error report file with more information is saved as:
# /Users/taki/Desktop/Preparation doctorat ERM/Projects/Julia4C/hs_err_pid24207.log
# 
# If you would like to submit a bug report, please visit:
# https://github.com/Homebrew/homebrew-core/issues
# 
zsh: abort      /usr/bin/env  --enable-preview -XX: ShowCodeDetailsInExceptionMessages -cp

I'm pretty sure that the error comes from env->CallBooleanMethod(java_util_object, java_add_method, a); because the add method requires an object, and a is jboolean.

I tried to cast the a variable but it didn't work as well.

CodePudding user response：

ArrayList<Boolean> is the same as just ArrayList. At runtime, the <Boolean> doesn't exist. This is called "type erasure".

The next thing to notice is that you did not try to add a Boolean (a kind of Object) but a primitive boolean. This probably gets interpreted as an object pointer and since it's not null it's the address of an Object - but true (the number 1) isn't a valid address of anything, and when the JVM dereferences it it crashes.

You need to get the static field Boolean.TRUE and add that to the ArrayList.

CodePudding user response：

I found a way to instantiate a java Boolean Object from c using Boolean.valueOf() function. I first get staticMethodId and then use it to create jobject and use the same object in the add method as follow:

JNIEXPORT jobject JNICALL Java_createArrayJNI_creatArray
  (JNIEnv *env, jobject thisObject) {
    std::vector<bool> cpp_vec;
    cpp_vec.push_back(true);
    cpp_vec.push_back(false);
    cpp_vec.push_back(true);
    
    jclass java_util_class = env->FindClass("java/util/ArrayList");
    jmethodID java_util_method_constructor = env->GetMethodID(java_util_class, "<init>", "()V");
    jmethodID java_add_method = env->GetMethodID(java_util_class, "add", "(Ljava/lang/Object;)Z");
    
    jobject java_util_object = env->NewObject(java_util_class, java_util_method_constructor, "");
    
    jclass bool_class = env->FindClass("java/lang/Boolean");
    jmethodID bool_init = env->GetStaticMethodID(bool_class, "valueOf", "(Z)Ljava/lang/Boolean;");
    
    for (int i=0; i< cpp_vec.size(); i  ){
      jboolean curr_element = cpp_vec[i];
      jobject bool_object = env->CallStaticObjectMethod(bool_class, bool_init, (jboolean) cpp_vec[i]);
      if (bool_object == NULL){
        std::cout << "Cannot instantiate the Boolean object";
        return NULL;
      } 
      env->CallBooleanMethod(java_util_object, java_add_method, bool_object);
    }
    return java_util_object;
}