Java语言和C语言混合编程(1)--Javanative关键字
可以将native方法比作Java程序同C程序的接口,其实现步骤为:
1、编写java源程序,add用native修饰
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package p2019.p06;
public class NativeAdd {
public native int add(int a,int b);
}
2、编译java程序,生成NativeAdd.class文件
[root@localhost java]# javac p2019/p06/NativeAdd.java
生成NativeAdd.class NativeAdd.java
3、javah生成.h文件
[root@localhost java]# javah p2019.p06.NativeAdd
生成p2019_p06_NativeAdd.h
1 /* DO NOT EDIT THIS FILE - it is machine generated */
2 #include
3 /* Header for class p2019_p06_NativeAdd */
4
5 #ifndef _Included_p2019_p06_NativeAdd
6 #define _Included_p2019_p06_NativeAdd
7 #ifdef __cplusplus
8 extern "C" {
9 #endif
10 /*
11 * Class: p2019_p06_NativeAdd
12 * Method: add
13 * Signature: (II)I
14 */
15 JNIEXPORT jint JNICALL Java_p2019_p06_NativeAdd_add
16 (JNIEnv *, jobject, jint, jint);
17
18 #ifdef __cplusplus
19 }
20 #endif
21 #endif
4、将生成的.h文件拷贝到/usr/java/jdk1.8.0_181-amd64/include/和/usr/java/jdk1.8.0_181-amd64/include/llinux目录下,编译C程序时用
5、编写C程序NativeAdd.c
1 #include
2 #include "p2019_p06_NativeAdd.h"
3 JNIEXPORT jint JNICALL Java_p2019_p06_NativeAdd_add(JNIEnv * _env, jobject _obj, jint _a, jint _b)
4 {
5 return _a+_b;
6 }
6、编译C程序,生成.so文件
gcc -I /usr/java/jdk1.8.0_181-amd64/include/ -I /usr/java/jdk1.8.0_181-amd64/include/linux/ NativeAdd.c -fPIC -shared -LD -o NativeAdd.so
7、编写java测试程序,调用NativeAdd.so
package p2019.p06;
public class NativeAddTest {
public static void main(String[] args){
System.out.println(System.getProperty("java.library.path"));
// System.loadLibrary("NativeAdd");这个方法找不到NativeAdd.so
System.load("/usr/lib/NativeAdd.so");
NativeAdd nativeAdd = new NativeAdd();
System.out.println(nativeAdd.add(1,2));
}
}
显示结果 3
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