jni jnienv GetBooleanArrayElements example c c++ java

Get<PrimitiveType>ArrayElements Routines - GetBooleanArrayElements

NativeType *Get<PrimitiveType>ArrayElements(JNIEnv *env,ArrayType array, jboolean *isCopy);

A family of functions that returns the body of the primitive array. The result is valid until the correspondingRelease<PrimitiveType>ArrayElements() function is called. Since the returned array may be a copy of the Java array, changes made to the returned array will not necessarily be reflected in the original array until Release<PrimitiveType>ArrayElements() is called. (GetBooleanArrayElements)

If isCopy is not NULL, then *isCopy is set to JNI_TRUE if a copy is made; or it is set to JNI_FALSE if no copy is made.

The following table describes the specific primitive array element accessors. You should make the following substitutions: (GetBooleanArrayElements)

• Replace Get<PrimitiveType>ArrayElements with one of the actual primitive element accessor routine names from the table.

• Replace ArrayType with the corresponding array type.

• Replace NativeType with the corresponding native type for that routine.

Regardless of how boolean arrays are represented in the Java VM, GetBooleanArrayElements() always returns a pointer tojbooleans, with each byte denoting an element (the unpacked representation). All arrays of other types are guaranteed to be contiguous in memory.

Table 4-9a Get<PrimitiveType>ArrayElements Family of Accessor Routines

Get<PrimitiveType>ArrayElements Routines	Array Type	Native Type
GetBooleanArrayElements()	jbooleanArray	jboolean
GetByteArrayElements()	jbyteArray	jbyte
GetCharArrayElements()	jcharArray	jchar
GetShortArrayElements()	jshortArray	jshort
GetIntArrayElements()	jintArray	jint
GetLongArrayElements()	jlongArray	jlong
GetFloatArrayElements()	jfloatArray	jfloat
GetDoubleArrayElements()	jdoubleArray	jdouble

LINKAGE:

Indices in the JNIEnv interface function table.

Table 4-9b Get<PrimitiveType>ArrayElements Family of Accessor Routines

Get<PrimitiveType>ArrayElements Routines	Index
GetBooleanArrayElements()	183
GetByteArrayElements()	184
GetCharArrayElements()	185
GetShortArrayElements()	186
GetIntArrayElements()	187
GetLongArrayElements()	188
GetFloatArrayElements()	189
GetDoubleArrayElements()	190

PARAMETERS of GetBooleanArrayElements

env: the JNI interface pointer.

array: a Java string object.

isCopy: a pointer to a boolean.

RETURNS of GetBooleanArrayElements

Returns a pointer to the array elements, or NULL if the operation fails.

Example of GetBooleanArrayElements

EDIT: This is how I convert the boolean array to unsigned char in C:

 jboolean *element = (*env)->GetBooleanArrayElements(env,chosen_packet,0);
 for(j = 0; j < sz; j++)
          src_pkt[j] = (unsigned char)element[j];

This src_pkt is acted upon and then I convert it back to jboolean .

EDIT2: This is how I convert the unsigned char array back to jboolean:

 jbooleanArray arr = (*env)->NewBooleanArray(env,sz);
 (*env)->SetBooleanArrayRegion(env,arr,0,sz,src_pkts);
 (*env)->DeleteLocalRef(env,arr);