如何在C/C++中调用Java （2）

Compiled from Demo.java
public class jni.test.Demo extends java.lang.Object {
 public static int COUNT;
 /*   I   */
 public java.lang.String msg;
 /*   Ljava/lang/String;   */
 private int counts[];
 /*   [I   */
 public jni.test.Demo();
 /*   ()V   */
 public jni.test.Demo(java.lang.String);
 /*   (Ljava/lang/String;)V   */
 public java.lang.String getMessage();
 /*   ()Ljava/lang/String;   */
 public int getCounts()[];
 /*   ()[I   */
 public void setCounts(int[]);
 /*   ([I)V   */
 public void throwExcp() throws java.lang.IllegalAccessException;
 /*   ()V   */
 static {};
 /*   ()V   */
}

/*
假设我们已经有一个jni.test.Demo的实例obj 
*/
jmethodID mid;
jclass cls = (*env)-> GetObjectClass (env, obj);	//获取实例的类定义
mid=(*env)->GetMethodID(env,cls,"getMessage"," ()Ljava/lang/String; ");
/*如果mid为0表示获取方法定义失败*/
jstring msg = (*env)-> CallObjectMethod(env, obj, mid);
/*
如果该方法是静态的方法那只需要将最后一句代码改为以下写法即可：
jstring msg = (*env)-> CallStaticObjectMethod(env, cls, mid);
*/

jfieldID (JNICALL *GetFieldID)
(JNIEnv *env, jclass clazz, const char *name, const char *sig);
jfieldID (JNICALL *GetStaticFieldID)
(JNIEnv *env, jclass clazz, const char *name, const char *sig);

public java.lang.String msg;
/*   Ljava/lang/String;   */

jfieldID field = (*env)->GetFieldID(env,obj,"msg"," Ljava/lang/String;");
jstring msg = (*env)-> GetObjectField(env, cls, field);	//msg就是对应Demo的msg
jfieldID field2 = (*env)->GetStaticFieldID(env,obj,"COUNT","I");
jint count = (*env)->GetStaticIntField(env,cls,field2);

jclass cls = (*env)->FindClass(env, "jni/test/Demo");
/** 
 首先通过类的名称获取类的定义，相当于Java中的Class.forName方法
*/
if (cls == 0) 
<error handler>
jmethodID mid = (*env)->GetMethodID(env,cls,"<init>","(Ljava/lang/String;)V ");
if(mid == 0)
<error handler>
jobject demo = jenv->NewObject(cls,mid,0);
/**
 访问构造函数必须使用NewObject的函数来调用前面获取的构造函数的定义
 上面的代码我们构造了一个Demo的实例并传一个空串null
*/

int i = 1;
jintArray array;	//定义数组对象
(*env)-> NewIntArray(env, 10);
for(; i<= 10; i++) 
(*env)->SetIntArrayRegion(env, array, i-1, 1, &i);

int i;
/* 获取数组对象的元素个数 */
int len = (*env)->GetArrayLength(env, array);
/* 获取数组中的所有元素 */
jint* elems = (*env)-> GetIntArrayElements(env, array, 0);
for(i=0; i< len; i++)
printf("ELEMENT %d IS %d\n", i, elems[i]);