jni jnienv CallObjectMethod example c c++ java

Call<type>Method Routines - CallObjectMethod

Call<type>MethodA Routines
Call<type>MethodV Routines

NativeType Call<type>Method(JNIEnv *env, jobject obj, jmethodID methodID, ...);

NativeType Call<type>MethodA(JNIEnv *env, jobject obj, jmethodID methodID, jvalue *args);

NativeType Call<type>MethodV(JNIEnv *env, jobject obj, jmethodID methodID, va_list args);

Methods from these three families of operations are used to call a Java instance method from a native method.They only differ in their mechanism for passing parameters to the methods that they call.(CallObjectMethod)

These families of operations invoke an instance (nonstatic) method on a Java object, according to the specified method ID. The methodID argument must be obtained by calling GetMethodID().

When these functions are used to call private methods and constructors, the method ID must be derived from the real class of obj, not from one of its superclasses. (CallObjectMethod)

Call<type>Method Routines

Programmers place all arguments that are to be passed to the method immediately following the methodID argument. The Call<type>Method routine accepts these arguments and passes them to the Java method that the programmer wishes to invoke.

Call<type>MethodA Routines

Programmers place all arguments to the method in an args array of jvalues that immediately follows the methodID argument. The Call<type>MethodA routine accepts the arguments in this array, and, in turn, passes them to the Java method that the programmer wishes to invoke.

Call<type>MethodV Routines

Programmers place all arguments to the method in an args argument of type va_list that immediately follows the methodID argument. The Call<type>MethodV routine accepts the arguments, and, in turn, passes them to the Java method that the programmer wishes to invoke.

The following table describes each of the method calling routines according to their result type. You should replace type in Call<type>Method with the Java type of the method you are calling (or use one of the actual method calling routine names from the table) and replace NativeType with the corresponding native type for that routine.

Table 4-3a Instance Method Calling Routines


Call<type>Method Routine Name	Native Type
`CallVoidMethod()` `CallVoidMethodA()` `CallVoidMethodV()`	void
`CallObjectMethod()` `CallObjectMethodA()` `CallObjectMethodV()`	jobject
`CallBooleanMethod()` `CallBooleanMethodA()` `CallBooleanMethodV()`	jboolean
`CallByteMethod()` `CallByteMethodA()` `CallByteMethodV()`	jbyte
`CallCharMethod()` `CallCharMethodA()` `CallCharMethodV()`	jchar
`CallShortMethod()` `CallShortMethodA()` `CallShortMethodV()`	jshort
`CallIntMethod()` `CallIntMethodA()` `CallIntMethodV()`	jint
`CallLongMethod()` `CallLongMethodA()` `CallLongMethodV()`	jlong
`CallFloatMethod()` `CallFloatMethodA()` `CallFloatMethodV()`	jfloat
`CallDoubleMethod()` `CallDoubleMethodA()` `CallDoubleMethodV()`	jdouble

LINKAGE:

Indices in the JNIEnv interface function table:

Table 4-3b Instance Method Calling Routines


Call<type>Method Routine Name	Index
`CallVoidMethod()` `CallVoidMethodA()` `CallVoidMethodV()`	61 63 62
`CallObjectMethod()` `CallObjectMethodA()` `CallObjectMethodV()`	34 36 35
`CallBooleanMethod()` `CallBooleanMethodA()` `CallBooleanMethodV()`	37 39 38
`CallByteMethod()` `CallByteMethodA()` `CallByteMethodV()`	40 42 41
`CallCharMethod()` `CallCharMethodA()` `CallCharMethodV()`	43 45 44
`CallShortMethod()` `CallShortMethodA()` `CallShortMethodV()`	46 48 47
`CallIntMethod()` `CallIntMethodA()` `CallIntMethodV()`	49 51 50
`CallLongMethod()` `CallLongMethodA()` `CallLongMethodV()`	52 54 53
`CallFloatMethod()` `CallFloatMethodA()` `CallFloatMethodV()`	55 57 56
`CallDoubleMethod()` `CallDoubleMethodA()` `CallDoubleMethodV()`	58 60 59

PARAMETERS:

env: the JNI interface pointer.

obj: a Java object.

methodID: a method ID.

Additional Parameter for Call<type>Method Routines:

arguments to the Java method.

Additional Parameter for Call<type>MethodA Routines:

args: an array of arguments.

Additional Parameter for Call<type>MethodV Routines:

args: a va_list of arguments.

RETURNS:

Returns the result of calling the Java method.

THROWS:

Exceptions raised during the execution of the Java method.

Example - CallObjectMethod

JNIEXPORT jint JNICALL 
Java_COM_novell_nsi_libsWrapper_BinderyJNI_NWScanObject  /* modified for example */
(
   JNIEnv   *env,
   jclass   obj, 
   jobject  objName,           // out, optional, StringBuffer
)
{
   nstr8 cObjectName [MAX_BINDERY_OBJECT_NAME_LEN];

   jstring javaString;   
   jclass cls;
   jmethodID mid;   
         
   .
   .
   .
   Some code to get cObjectName
         
   javaString = (jstring)(*env)->NewStringUTF(env, (const char *)cObjectName);

   cls = (*env)->GetObjectClass(env, objName);
   mid = (*env)->GetMethodID(env, cls, "append","(Ljava/lang/String;)Ljava/lang/StringBuffer;");
   if (0 == mid)
   {
      printf("GetMethodID returned 0\n");
      return(-1);
   }
   (*env)->CallObjectMethod(env, objName, mid, javaString);

Example source code bank

Saturday, April 20, 2013