Wednesday, April 24, 2013

jni jnienv GetCharArrayElements example c c++ java


Get<PrimitiveType>ArrayElements Routines - GetCharArrayElements


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. (GetCharArrayElements)

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: (GetCharArrayElements)

  • 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 GetCharArrayElements

env: the JNI interface pointer.

array: a Java string object.

isCopy: a pointer to a boolean.

RETURNS of GetCharArrayElements

Returns a pointer to the array elements, or NULL if the operation fails.
Example of GetCharArrayElements
jobject obj = ... // This is the object you want to call the method on
jcharArray arr = (jcharArray) (*env)->CallObjectMethod(env, obj, getVal);
int count = (*env)->GetArrayLength(env, arr);
jchar* chars = (*env)->GetCharArrayElements(env, arr, 0);