JNI测试-java调用c算法并返回java调用处-1到20阶乘的和

 1 public class FactorialJava {
 2 
 3     public native long factorial(int n);
 4 
 5     //evaluate the elapse time.and the execution result.
 6     public long elapse() {
 7         long start = System.currentTimeMillis();
 8 
 9         // code executing time.
10         long sumResult = factorial(20);
11 
12         System.out.println("sum_result:" + sumResult);
13 
14         long end = System.currentTimeMillis();
15         return end - start;
16     }
17 
18     //load the dll library before executing conductive code.
19     static {
20         System.loadLibrary("FactorialDll");
21     }
22 
23     public static void main(String[] args) {
24         FactorialJava fac = new FactorialJava();
25         System.out.println("耗时: " + fac.elapse() + " 毫秒");
26     }
27 
28 }

 1 jlong
 2 recesive_fac(jint n) {
 3     if(n == 1)
 4         return 1;
 5     else
 6     {
 7         return n * recesive_fac(n - 1);
 8     }
 9 }
10 
11 //使用jni循环递归过程,将结果返回java调用处.
12 JNIEXPORT jlong JNICALL Java_FactorialJava_factorial
13   (JNIEnv *env, jobject obj, jint n) {
14     jlong sum = 0;    
15     //const jint n = 20;
16     for(int i = 1; i <= n; i++) {
17         sum += recesive_fac(i);
18     }
19     
20     return sum;
21 }