A native method has the same syntax as an abstract method, but where is it implemented?

解決方案

What are native methods in Java and where should they be used?

Once you see a small example, it becomes clear:

Main.java:

public class Main {

public native int intMethod(int i);

public static void main(String[] args) {

System.loadLibrary("Main");

System.out.println(new Main().intMethod(2));

}

}

Main.c:

#include

#include "Main.h"

JNIEXPORT jint JNICALL Java_Main_intMethod(

JNIEnv *env, jobject obj, jint i) {

return i * i;

}

Compile and run:

javac Main.java

javah -jni Main

gcc -shared -fpic -o libMain.so -I${JAVA_HOME}/include \

-I${JAVA_HOME}/include/linux Main.c

java -Djava.library.path=. Main

Output:

4

Tested on Ubuntu 14.04 with Oracle JDK 1.8.0_45.

So it is clear that it allows you to:

call a compiled dynamically loaded library (here written in C) with arbitrary assembly code from Java

and get results back into Java

This could be used to:

write faster code on a critical section with better CPU assembly instructions (not CPU portable)

make direct system calls (not OS portable)

with the tradeoff of lower portability.

It is also possible for you to call Java from C, but you must first create a JVM in C: How to call Java functions from C++?

Example on GitHub for you to play with.

總結

以上是生活随笔為你收集整理的java的方法是什么用,Java中的本机方法是什么？它们应该在何处使用？的全部內容，希望文章能夠幫你解決所遇到的問題。

如果覺得生活随笔網站內容還不錯，歡迎將生活随笔推薦給好友。