Develop Reference

Interfacing with Java Functions in Haxe

I am trying to call an external Java function from Haxe using "extern".
Haxe Code :
extern class Ext
{
public static function test():String;
}
class Sample
{
public static function main()
{
trace(Ext.test());
}
}
Java Code :
public class Ext
{
public static String test()
{
return "Hello";
}
}
Both Sample.hx and Ext.java files are in the same folder.
When I try to execute haxe -main Sample -java Sample, I get the following error.
C:\Users\ila5\Desktop\CPP>haxe -main Sample -java Sample
haxelib run hxjava hxjava_build.txt --haxe-version 3201 --feature-level 1
javac.exe "-sourcepath" "src" "-d" "obj" "-g:none" "#cmd"
src\haxe\root\Sample.java:33: error: cannot find symbol
haxe.Log.trace.__hx_invoke2_o(0.0, haxe.root.Ext.test(), 0.0, new haxe.lang.DynamicObject(new java.lang.String[]{"className", "fileName", "methodName"}, new java.lang.Object[]{"Sample", "Sample.hx", "main"}, new java.lang.String[]{"lineNumber"}, new double[]{((double) (((double) (10) )) )}));
^
symbol: class Ext
location: package haxe.root
1 error
Compilation error
Native compilation failed
Error: Build failed
I would like to understand why the build failed. Any ideas?

I am not sure you might need to reference your Java code with -lib or something else?
But generally with Java target it's much simpler to just use a jar file. By typing haxe --help you will see the relevant command listed, I have never had a need to hand write externs for the Java target.
-java-lib <file> : add an external JAR or class directory library

The reason it fails is explained here
https://groups.google.com/forum/#!topic/haxelang/EHeoGN_Ppvg
I tried setting up with class paths and various options but did not get a solution, I think it's just a bit fiddly to do externs on the java target by hand. Really it's better to use Java compiler to create jars and let haxe auto generate the externs unless you get an issue then report it to hxJava repository.

Use -java-lib.
# build.sh
haxe Main.hx -main Main -java-lib javalib/ -java out
,
// ./Main.hx
import external.*;
class Main {
public static function main() {
trace(external.ExternalClass.myFunction());
}
}
,
// ./javalib/external/ExternalClass.java
package external;
public class ExternalClass {
public static String myFunction() {
return "External Java function";
}
}
,
./javalib/external/ExternalClass.class is the output of javac ExternalClass.java

Using native code in java

I want to create c library and use it in my java code on an Linux OS. I'm trying to understand and implement natural library concept.
I'm following this tutorial
http://diglib.stanford.edu:8091/~testbed/doc/JavaUsage/JNI/tutorial.txt
Which is helpful me to understand concept a little. However, I get errors when I try to do it myself. I searced for errors I am getting but none of solutions helped.
Main class code and class for natural library I wrote is as follows:
package natLib;
import natLib.getKeyPressed;
public class main {
public static void main(String[] args) {
getKeyPressed natlab=new getKeyPressed();
char c=natlab.keyboardPressedKey();
}
}
package natLib;
public class getKeyPressed {
static {
System.loadLibrary("natlab");
}
public native char keyboardPressedKey();
}
when I write "javac main.java"
I get errors like
"main.java:6: error: cannot find symbol
getKeyPressed natlab=new getKeyPressed();"
And when I skip for main and just do javac prcess for class with native method, try to obtain a header file
javah -jni getKeyPressed.class
Although there is a file as getKeyPressed.class, I get errors like:
"Exception in thread "main" java.lang.IllegalArgumentException: Not a valid class name: getKeyPressed.class"
I try it without .class extention it says
"Error: Could not find class file for 'getKeyPressed'."
It says that even when I make getKeyPressed class file by copying getKeyPressed.class.
It seems I am making a major mistake, any suggestions to solve this?

javah expects a fully qualified classname. (e.g. natLib.getKeyPressed, not just getKeyPressed)

Cannot run my own Java Package

I want to learn to write my own packages so I'm not also relient on an IDE, which I feel I have became. The problem is I cannot figure out how to run my own package, or what the proper method is to run your own package.
Here's a resource I used to learn some basics: http://javaworkshop.sourceforge.net/chapter3.html
Here's my current file structure:
Main.java
/src
projectaqua/
GameFrame.java
/classes
projectaqua/
GameFrame.class
I ran the command in the root directory of the project:javac -d ./classes/ ./src/projectaqua/*.java
I originally created a Main file in the /src/projectaqua directory and attempted to run the file. I was given this error:
Main.java:1: error: package projectaqua does not exist
import projectaqua.GameFrame;
I tried running the application in the /classes/projectaqua directory when compiling the Main file with the package, which gave me a class not defined error.
This compiled my package, the problem I'm facing is I don't understand how you are supposed to import your own package to run it, and where would the file to run the package be?
From what I've learned in school, when writing a GUI application we create a class that has a main function in it to instantiate the frame, and that's it's only job. Where would this be in this structure?
Intuitively it seems that file would be outside of the src files, but I feel like that removes the purpose of the src files. I haven't found anything useful on stackoverflow to this topic, if you do or have please point me in that direction.
More source code:
GameFrame Class:
package projectaqua;
import javax.swing.JFrame;
public class GameFrame extends JFrame
{
private int WINDOW_HEIGHT = 500;
private int WINDOW_WIDTH = 500;
private String title = "Project Aqua";
private boolean isVisible = true;
public GameFrame()
{
// Basic Window Defaults
setSize(WINDOW_WIDTH, WINDOW_HEIGHT);
setTitle(this.title);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
// Content Pane junk
// Will be added
setVisible(this.isVisible);
}
}
The Main class
import projectaqua.GameFrame;
public class Main
{
public static void main(String[] args)
{
GameFrame launch = new GameFrame();
}
}

I now see your problem.
In your question you were not clear that you had trouble running v. compiling. Had you posted this error trace it would have been immediately clear to me what your problem is:
unrollme-dev-dan:projectaqua Dan$ java Main
Exception in thread "main" java.lang.NoClassDefFoundError: Main (wrong name: projectaqua/Main)
Also note that had you Googled NoClassDefFoundError would have found this. The moral here is: understand and research your exact error.
Anyway
unrollme-dev-dan:classes java projectaqua/Main
is what you want. Notice the change of directory. I never bothered to understand why, has to do with relationship between package hierarchy and file structure hierarchy.
Java had two choices when designed: Assume the thing you are talking about is in the global package (yuck!) or try to guess what package it is in. It treats any folder below your working directory as packages. So even though it found a Main class in the directory from which you were running it did not find a Main class in the namespace corresponding to the directory . i.e. the global one.
When you run from one directory up and tell it to run something in projectaqua/ it is now looking for classes starting with projectaqua.
Alternately if you run
unrollme-dev-dan:projectaqua java projectaqua.Main
It looks for the right thing.

try this command at the root of your project
javac -cp ./classes -d ./classes ./src/projectaqua/*.java
Also make sure both your Main.java and GameFrame.java has package projectaqua; at the beginning

Exception in thread "main" java.lang.NoClassDefFoundError: wrong name

My file directory:
project/src/m2mcom/entities/AutomatedTelnetClient.java
/web/Simple.java
/org/apache/commons/net/telnet/TelnetClient.java
The source code of the Simple.java:
package m2mcom.web;
import m2mcom.entities.AutomatedTelnetClient;
import java.util.*;
import java.io.*;
public class Simple {
public static void main(String [] args) {
try {
AutomatedTelnetClient telnet = new AutomatedTelnetClient();
String answer = telnet.request();
System.out.println(answer);
} catch (Exception e) {
System.err.println("Error");
}
}
}
And when I execute Simple.class, without any errors of compilation, I get this error message:
C:\Users\Victor\Desktop\project2\src\m2mcom\web>java Simple
Exception in thread "main" java.lang.NoClassDefFoundError: Simple (wrong name: m
2mcom/web/Simple)
Does anyone know how to solve this?

You're executing the command in the wrong folder, with the wrong classname. You need to use the fully qualified name (FQN) when running a Java class. And of course, you have to be in the right directory. In your example, the FQN of your class is m2mcom.web.Simple (combination of the package m2mcom.web and the simple name Simple).
As far as deducing the right directory, your classes are stored in a hierarchical folder structure, which basically starts in C:\Users\Victor\Desktop\project2\src.
So to correctly execute your program, from C:\Users\Victor\Desktop\project2\src, do;
java m2mcom.web.Simple

package m2mcom.web;
remove above line and recompile it.
when you run your code in netbeans it including in a m2mcom.web package.that is not in your class file.

So you have to be in the directory right above the package name when you execute the java command which should be in the form packagename.classname without the .class suffix.

Java Command Line Trouble with Reading a Class from a Jar Archive

I am trying to run a java based tool using a command line syntax as the following: java -cp archive.jar archiveFolder.theMainClassName.Although the class I am searching for, a main class, "theMainClassName" is in the archive.jar and in the archiveFolder given at input, I keep getting the error that my class is not seen. Does anybody have any ideas concerning this problem? Thank you in advance

Here's a concrete example of what does work, so you can compare your own situation.
Take this code and put it anywhere, in a file called MainClass.java. (I've assumed a directory called src later. Normally you'd arrange the source to match the package, of course.)
package archiveFolder;
public class MainClass
{
public static void main(String[] args)
{
System.out.println("I'm MainClass");
}
}
Then run each of these commands:
# Compile the source
javac -d . src/MainClass.java
# Build the jar file
jar cf archive.jar archiveFolder
# Remove the unpackaged binary, to prove it's not being used
rm -rf archiveFolder # Or rmdir /s /q archiveFolder on Windows
# Execute the class
java -cp archive.jar achiveFolder.MainClass
The result:
I'm MainClass
How are you building your jar file? Is the code in the appropriate package?

Does theMainClassName class have the following package line at the top:
package archiveFolder
You need the class file to be in the same directory structure as the declared package. So if you had something like:
org/jc/tests/TestClass.class
its source file would have to look like this:
package org.jc.tests;
public class TestClass {
public static void main(String[] args) {
System.out.printf("This is a test class!\n");
}
}
Then you could use the following to create the jar file and run it from the command line (assuming the current directory is at the top level, just above org):
$ jar -cf testJar.jar org/jc/tests/*.class
$ java -cp testJar.jar org.jc.tests.TestClass

Perhaps with java -jar archive.jar?
Of course, it supposes the manifest points to the right class...
You should give the exact message you got, it might shed more light.
EDIT: See Working with Manifest Files: The Basics for information on setting the application entry point (Main class) in your jar manifest file.

Usually this happens when a dependent class (static member) is not found - like this, using log4j:
public class MyClass {
private static Logger log = Logger.getLogger("com.example");
}
The reason is that the initialization of such a static member can be understood as part of the class loading - errors causing the class not to be available (loadable), resulting in the error you described.
Static constructors are another possible reason:
public class MyClass {
static {
// <b>any</b> error caused here will cause the class to
// not be loaded. Demonstrating with stupid typecast.
Object o = new String();
Integer i = (Integer) o;
}
}

I think others have covered some common stuff here. I'd jar tf the jar and make sure the class is listed. I'd also double-check that the class is public and the method is "public static void main(String[] arg)".