JNI Help

**jsobel** · 09-19-2012, 11:08 PM

I an trying to import some native code into my java program to enable changing the color of the console and wiping it,but for some reason it fails when generating the c++ header file please watch the video and tell me if you see what i am doing wrong

**jsobel** · 09-20-2012, 01:21 AM

if no one can figure out why this doesnt work can someone javah this for me and post the header file

Java Code:

public class Console
{
	static
	{
		System.loadLibrary("console");
	}
	
	/**
	 * Wipes all text off the console screen
	 */
	public native static void clearScreen();
	
	private native static void setColor(char background, char foreground);
	
	/**
	 * Sets the color of the console in hex the java program is running on may not work on all consoles
	 * @param background color
	 * @param foreground color
	 */
	public static void setColor(byte background, byte foreground)
	{
		String background2 = Integer.toHexString(background);
		String foreground2 = Integer.toHexString(foreground);
		char f=foreground2.charAt(0);
		char b=background2.charAt(0);
		setColor(b,f);
	}
}

**Fubarable** · 09-20-2012, 01:44 AM

I just did a manual javah run and got this result:

yr12_m09_b_Console.h

Java Code:

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class yr12_m09_b_Console */

#ifndef _Included_yr12_m09_b_Console
#define _Included_yr12_m09_b_Console
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     yr12_m09_b_Console
 * Method:    clearScreen
 * Signature: ()V
 */
JNIEXPORT void JNICALL Java_yr12_m09_b_Console_clearScreen
  (JNIEnv *, jclass);

/*
 * Class:     yr12_m09_b_Console
 * Method:    setColor
 * Signature: (CC)V
 */
JNIEXPORT void JNICALL Java_yr12_m09_b_Console_setColor
  (JNIEnv *, jclass, jchar, jchar);

#ifdef __cplusplus
}
#endif
#endif

Note though that my Console class uses this package:

package yr12.m09.b;

and the package name will be part of the java name in the header file above. above.

**jsobel** · 09-20-2012, 02:29 AM

im confused about what i have to do now that you have put it in a package named yr12_m09_b

**jsobel** · 09-23-2012, 03:43 AM

i hate to bother people but can someone javah this for me it still wont work

Java Code:

public class Console
{
	private Console()
	{
		
	}
	
	static
	{
		System.loadLibrary("console");
	}
	
	/**
	 * Sets the console color back to it's defaults
	 */
	public static void restoreColor()
	{
		setColor(0,7);
	}
	
	/**
	 * Wipes all text off the console screen
	 */
	public native static void clearScreen();
	
	private native static void setColor(char background, char foreground);
	
	/**
	 * Sets the color of the console in hex the java program is running on may not work on all consoles
	 * @param background color
	 * @param foreground color
	 */
	public static void setColor(int background, int foreground)
	{
		String background2 = Integer.toHexString(background);
		String foreground2 = Integer.toHexString(foreground);
		char f=foreground2.charAt(0);
		char b=background2.charAt(0);
		setColor(b,f);
	}
	
	/**
	 * Halts the console IO until the user presses a key on the console 
	 */
	public static native void pause();
	}

**Fubarable** · 09-23-2012, 05:49 AM

You need to be able to use these tools yourself if you're going to progress. Are you calling javah from the command line? If so, what's wrong with this effort? What's not working right? What error messages are you getting?

**jsobel** · 09-23-2012, 05:45 PM

watch the video mostly invalid class exceptions idk

**Fubarable** · 09-23-2012, 06:03 PM

The video doesn't work for me, poor resolution. If you still need our help, consider describing exactly what's going wrong including showing your error messages. If you are running javah on the command line, you can copy the entire text from the cmd window and paste it here.

**jsobel** · 09-23-2012, 06:42 PM

I am running these commands and get this error
javac Console.java
javah -jni Console.class

C:\Users\Joshy\Desktop\console>javac Console.java

C:\Users\Joshy\Desktop\console>javah -jni Console.class

Exception in thread "main" java.lang.IllegalArgumentException: Not a valid class
name: Console.class
at com.sun.tools.javac.api.JavacTool.getTask(JavacToo l.java:177)
at com.sun.tools.javac.api.JavacTool.getTask(JavacToo l.java:68)
at com.sun.tools.javah.JavahTask.run(JavahTask.java:5 09)
at com.sun.tools.javah.JavahTask.run(JavahTask.java:3 35)
at com.sun.tools.javah.Main.main(Main.java:46)

**sabre150** · 09-23-2012, 08:45 PM

Run

javah - h

You will then see the line -
<classes> are specified with their fully qualified names.

"Fully qualified" means you need the package and class name. e.g. your.package.Console

**jsobel** · 09-23-2012, 10:10 PM

im using the default package

**Fubarable** · 09-23-2012, 10:16 PM

I wouldn't do Console.class but would simply use Console and would probably add the classpath option, -cp . For example

Java Code:

javah -cp . Console

Note the period before Console and the spaces around the period, all very important. Again note that I'm using the class's name, Console, but without the .class extension.

**jsobel** · 09-23-2012, 11:29 PM

It worked thanks so much

**Fubarable** · 09-23-2012, 11:31 PM

You're welcome. Glad you've got it working. Note that the -h option as was mentioned above gives you "help" information on how to run javah (as noted above).