jniarraywrapperimpl.cpp

高级java2 大学教程(含源码,经典的Java学习教程

// JNIArrayWrapperImpl.cpp
// Implements the header created by java to integrate with JNI
// Creates a new array of random integers and returns it to java.

// C++ core header
#include <stdlib.h>
#include <time.h>

// header produced by javah
#include "JNIArrayWrapper.h"

// creates and fills 2 arrays
JNIEXPORT jintArray JNICALL Java_JNIArrayWrapper_newRandomArray
                ( JNIEnv * env, jobject thisObject, jint size )
{
   srand( time( NULL ) );

   // boolean to determine if elements are copied
   jboolean isCopy;

   // temporary variables
   int randomInt;
   jobject randomIntegerObject;

   // locate object and constructor
   jclass integerClass = env->FindClass( "java/lang/Integer" );
   jmethodID mid = 
      env->GetMethodID( integerClass, "<init>", "(I)V" );
   
   // build new Integer array of length size
   jobjectArray objectArray = 
      env->NewObjectArray( size, integerClass, NULL );
   
   // create new primitive int array
   jintArray intArray = env->NewIntArray( size );
   
   // return pointer to array of elements
   jint * intArrayPointer = 
      env->GetIntArrayElements( intArray, &isCopy );
   
   // fill arrays with pseudo random numbers
   for ( int i = 0 ; i < size ; i++ ) {

      // create random int
      randomInt = rand() % 100;
      
      // create Integer with random int
      randomIntegerObject =  
         env->NewObject( integerClass, mid, randomInt );
      
      // add element to Integer array
      env->SetObjectArrayElement( 
         objectArray, i, randomIntegerObject );

      // assign random int to primitive array
      intArrayPointer[ i ] = randomInt;
   }

   // if JNI made a copy, release it and update Java
   if ( isCopy == JNI_TRUE ) {
      env->ReleaseIntArrayElements( intArray, intArrayPointer, 0 );
   }

   return intArray;
}

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