JNI Small Test Sledgehammer

Jni:

JNI is the abbreviation for Java Native Interface, which provides a number of APIs that enable the communication of Java and other languages (primarily c&c++). Starting with Java1.1, the JNI standard becomes part of the Java platform, which allows Java code to interact with code written in other languages. JNI was initially designed for local compiled languages, especially C and C + +, but it does not prevent you from using other programming languages, as long as the calling convention is supported. Using Java to interact with locally compiled code often loses platform portability. However, in some cases it is acceptable and even necessary. For example, use some old libraries to interact with the hardware, the operating system, or to improve the performance of the program. The JNI standard should at least ensure that local code can work in any Java Virtual machine environment.

Application:

First:

Write the class, and add the native method, not life does not describe the specific implementation.

Ex

1  PackageKg.tom;2  Public classMyjni {3 4     Public  native void display (); 5      Public native double sum (double x,double y);6       7 8      Static {9System.loadlibrary ("Sum");Ten         } One       A  -      Public Static voidMain (string[] args) { -  the          NewMyjni (). display (); -System.out.println (NewMyjni (). SUM (2.0, 3.0)); -     -         +     } -       +       A}

Second:

First, the Javac command compiles the class file to generate the classes byte code, and the Javah command generates the. h file from the class file.

Ex

Third:

Write the native C file.

//Required header file jni.h#include <jni.h>//If you do not set the path of the jni.h to path, you can copy it to the same directory as the C file and modify it to #include "jni.h"//Import the local methods we need to implement#include "kg_tom_myjni.h"//need to be in the C file directory#include<stdio.h>Jniexportvoidjnicall Java_kg_tom_myjni_display (jnienv*env, Jobject obj) {printf ("Hello World tom!!"); return;} Jniexport jdouble jnicall java_kg_tom_myjni_sum (jnienv*env, Jobject obj, jdouble A, jdouble b) {    returnA +b;}

Four:

Compiled into a linked file, which is translated into DLL files under Windows and translated into so files under Linux.

Gcc-wall-d_jni_implementation_-wl,--kill-at-id:/java/include–id:/java/include/win32-shared-o sum.dll java_sum_n Ative.c

Command	Simple Introduction
-wall-d_jni_implementation_	Compile our C file into a DLL
-WL,--Kill-at	Because MinGW is separated by the @ by default, it causes the JNI mechanism to be unreadable, so it should be deleted. MinGW Official website explanation
Id:/java/include–id:/java/include/win32	Import the header file that we used for JNI required ... Drive letter, folder to modify itself
-shared-o	Output configuration, the first parameter is our output name (random), the second parameter is our C file (random)

Five:

Run JNI, put the compiled DLL into the project root directory, note that it is not the code root directory.

Execution effect:

JNI Small Test Sledgehammer