native_Keyword
native Java Keyword with Examples
The native keyword is applied to a method to indicate that the method is implemented in native code using JNI (Java Native Interface).
Key points about native Java Keyword
- The native keyword may be applied to a method to indicate that the method is implemented in a language other than Java.
- The native keyword is used to declare a method which is implemented in platform-dependent code such as C or C++. When a method is marked as native, it cannot have a body and must ends with a semicolon instead.
- The Java Native Interface (JNI) specification governs rules and guidelines for implementing native methods, such as data type conversion between Java and the native application.
native Java Keyword Example
- Main.java
Let’s create a Java Main.java class:
public class Main {
public native int square(int i);
public static void main(String[] args) {
System.loadLibrary("Main");
System.out.println(new Main().square(2));
}
}
- Main.c:
Let’s create sample code in C language.
#include <jni.h>
#include "Main.h"
JNIEXPORT jint JNICALL Java_Main_square(
JNIEnv *env, jobject obj, jint i) {
return i * i;
}
- Compile and run:
sudo apt-get install build-essential openjdk-7-jdk
export JAVA_HOME='/usr/lib/jvm/java-7-openjdk-amd64'
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
