Java Native Access - Example

Example

The following program loads the local C standard library implementation and uses it to call the printf function.

Note: The following code is portable and works the same on Windows and Linux / Unix / Mac OS X platforms.

import com.sun.jna.Library; import com.sun.jna.Native; import com.sun.jna.Platform; /** Simple example of native library declaration and usage. */ public class HelloWorld { public interface CLibrary extends Library { CLibrary INSTANCE = (CLibrary) Native.loadLibrary( (Platform.isWindows ? "msvcrt" : "c"), CLibrary.class); void printf(String format, Object... args); } public static void main(String args) { CLibrary.INSTANCE.printf("Hello, World\n"); for (int i = 0; i < args.length; i++) { CLibrary.INSTANCE.printf("Argument %d: %s\n", i, args); } } }

The following program loads the C POSIX library and uses it to call the standard mkdir function.

Note: The following code is portable and works the same on POSIX standards platforms.

import com.sun.jna.Library; import com.sun.jna.Native; /** Simple example of native C POSIX library declaration and usage. */ public class exampleOfPOSIX { public interface POSIX extends Library { public int chmod(String filename, int mode); public int chown(String filename, int user, int group); public int rename(String oldpath, String newpath); public int kill(int pid, int signal); public int link(String oldpath, String newpath); public int mkdir(String path, int mode); public int rmdir(String path); } public static void main(String args) { POSIX posix = (POSIX) Native.loadLibrary("c", POSIX.class); posix.mkdir("/tmp/newdir", 0777); posix.rename("/tmp/newdir","/tmp/renamedir"); } }

The program below loads the Kernel32.dll and uses it to call the Beep and Sleep functions.

Note: The following code works only on Windows platforms.

import com.sun.jna.Library; import com.sun.jna.Native; /** Simple example of Windows native library declaration and usage. */ public class BeepExample { public interface Kernel32 extends Library { // FREQUENCY is expressed in hertz and ranges from 37 to 32767 // DURATION is expressed in milliseconds public boolean Beep(int FREQUENCY, int DURATION); public void Sleep(int DURATION); } public static void main(String args) { Kernel32 lib = (Kernel32) Native.loadLibrary("kernel32", Kernel32.class); lib.Beep(698, 500); lib.Sleep(500); lib.Beep(698, 500); } }