JNI:GetIntArrayElements()的一些问题

[duyiwuer2009]

	// example-1: GetStringUTFChars()
	public class Prompt
	{
		// native method that prints a prompt and reads a line
		private native String getLine(String prompt);
		public static void main(String args[])
		{
			Prompt p = new Prompt();
			String temp = new String("Type a line: ");
			String input = p.getLine(temp);
			System.out.println("User typed: " + input);
			System.out.println(temp);
		}
		static
		{
			System.loadLibrary("Prompt");
		}
	}
	/*
	javac Prompt.java
	javah Prompt
	get a file: Prompt.h
	*/

	#include "Prompt.h"
	#include <stdio.h>
	#include <string.h>
	JNIEXPORT jstring JNICALL Java_Prompt_getLine (JNIEnv *env, jobject obj, jstring prompt)
	{
		char buf[128];
		const jbyte *str;
		jboolean isCp;
		str = (*env)->GetStringUTFChars(env, prompt, &isCp);
		if (str == NULL) {
			return NULL; /* OutOfMemoryError already thrown */
		}
		if(isCp == JNI_TRUE)
		{
			strcpy(str,"12345");
		}
		printf("%s", str);
		(*env)->ReleaseStringUTFChars(env, prompt, str);
		/* We assume here that the user does not type more than
		 * 127 characters */
		scanf("%s", buf);
		return (*env)->NewStringUTF(env, buf);
	}
	/*
	set java_inc=E:\FILES\java\jdk1.6.0_29\include
	cl -I%java_inc% -I%java_inc%\win32 -LD Prompt.c -FePrompt.dll
	*/
	/* output
	the output of running class Prompt.class:
	12345jdkfjkdjfkdf
	User typed: jdkfjkdjfkdf
	Type a line:

	the output demonstrates that String instance temp did not changed, and isCopy is JNI_TRUE
	*/


	// example-2: GetIntArrayElements()
	public class TestJNI
	{
		public native void intArray(int[] ii);
		public static void main(String[] args)
		{
			System.loadLibrary("TestJNI");
			TestJNI jni = new TestJNI();
			int[] ii = new int[4];
			for(int i = 0; i < ii.length; i++)
			{
				ii[i] = i;
			}
			jni.intArray(ii);
			for(int i = 0; i < ii.length; i++)
			{
				System.out.println(ii[i]);
			}
		}
	}
	/*
	output:
	isCopy: 1
	100
	101
	102
	103

	the output shows that ii has been changed, but isCopy is JNI_TRUE
	*/

	#include "TestJNI.h"
	#include <stdio.h>
	JNIEXPORT void JNICALL Java_TestJNI_intArray(JNIEnv *env, jobject obj, jintArray intArr)
	{
		jboolean isCp;
		int i;
		jsize len = (*env)->GetArrayLength(env, intArr);
		jint *arr = (*env)->GetIntArrayElements(env, intArr, &isCp);
		if(isCp == JNI_TRUE)
		{
			printf("isCopy: JNI_TRUE\n");
		}
		for(i = 0; i < len; i++)
		{
			arr[i] = 100 + i;
		}
		(*env)->ReleaseIntArrayElements(env, intArr, arr, 0);
	}
	/*
	output:
	isCopy: 1
	100
	101
	102
	103

	the output shows that ii has been changed, but isCopy is JNI_TRUE
	*/

在example-2中，isCopy 被设置为 JNI_TRUE，表示arr 指向新分配的内存，修改arr 将不影响intArr ，但输出结果却是intArr 改变了，为什么？
在example-1中，prompt 的只还是 “Type a line:”，这是合理的