Get<PrimitiveType>ArrayElements Routines - GetDoubleArrayElements
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. (GetDoubleArrayElements)
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: (GetDoubleArrayElements)
- 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
LINKAGE:
Indices in the JNIEnv interface function table.
Table 4-9b Get<PrimitiveType>ArrayElements Family of Accessor Routines
PARAMETERS of GetDoubleArrayElements
env: the JNI interface pointer.array: a Java string object.isCopy: a pointer to a boolean.RETURNS of GetDoubleArrayElements
Returns a pointer to the array elements, or
NULL if the operation fails.
Example of GetDoubleArrayElements
// Get the class
jclass mvclass = env->GetObjectClass( *cls );
// Get method ID for method getSomeDoubleArray that returns a double array
jmethodID mid = env->GetMethodID( mvclass, "getSomeDoubleArray", "()[D");
// Call the method, returns JObject (because Array is instance of Object)
jobject mvdata = env->CallObjectMethod( *base, mid);
// Cast it to a jdoublearray
jdoubleArray * arr = reinterpret_cast<jdoubleArray*>(&mvdata)
// Get the elements (you probably have to fetch the length of the array as well
double * data = env->GetDoubleArrayElements(*arr, NULL);
// Don't forget to release it
env->ReleaseDoubleArrayElements(*arr, data, 0);JNIEXPORT void JNICALL Java_Test_process(JNIEnv * env, jclass c, jobject jc) {
jclass jcClass = env->GetObjectClass(jc);
jfieldID iId = env->GetFieldID(jcClass, "i", "I");
// This way we can get and set the "i" field. Let's double it:
jint i = env->GetIntField(jc, iId);
env->SetIntField(jc, iId, i * 2);
// The jfieldID of the "a" field (byte array) can be got like this:
jfieldID aId = env->GetFieldID(jcClass, "a", "[B");
// Get the object field, returns JObject (because Array is instance of Object)
jobject mvdata = env->GetObjectField (jc, aID);
// Cast it to a jdoublearray
jdoubleArray * arr = reinterpret_cast<jdoubleArray*>(&mvdata)
// Get the elements (you probably have to fetch the length of the array as well
double * data = env->GetDoubleArrayElements(*arr, NULL);
// Don't forget to release it
env->ReleaseDoubleArrayElements(*arr, data, 0);
}