Develop Reference

Problem connecting Java and Prolog with JPL

I wanted to connect Java and Swi Prolog together using JPL.
When I added the library to my project on Intellij the code compiled and when I tried to run a query I got a runtime error:
Exception in thread "main" java.lang.UnsatisfiedLinkError: no jpl in java.library.path: [C:\Program Files\Java\jdk-12\bin, C:\WINDOWS\Sun\Java\bin, C:\WINDOWS\system32, C:\WINDOWS, c:\swipl\bin, ${env_var:PATH}, .]
at java.base/java.lang.ClassLoader.loadLibrary(ClassLoader.java:2660)
at java.base/java.lang.Runtime.loadLibrary0(Runtime.java:827)
at java.base/java.lang.System.loadLibrary(System.java:1902)
at org.jpl7.JPL.loadNativeLibrary(JPL.java:114)
at org.jpl7.fli.Prolog.<clinit>(Prolog.java:71)
at org.jpl7.Query.open(Query.java:369)
at org.jpl7.Term.textToTerm(Term.java:155)
at org.jpl7.Query.<init>(Query.java:169)
at Main.main(Main.java:7)
I have the swi prolog 64 bit.
I've tried uninstalling it and use the 32 bit but it did not work.
What I did so far:
I added SWI_HOME_DIR to my Environment Variables.
I also added the swi path to Path variable.
I added the jpl library to my project (and it added it successfully).
The code I was trying to run:
import org.jpl7.*;
import java.util.Map;
public class Main {
public static void main(String[] args) {
Query q = new Query("true");
q.hasSolution();
Map<String,Term>[] res = q.allSolutions();
for (int i = 0; i < res.length; i++) {
System.out.println(res[i]);
}
}
}

So, is jpl.dll in any of the listed directories:
C:\Program Files\Java\jdk-12\bin ... probably not
C:\WINDOWS\Sun\Java\bin ... probably not
C:\WINDOWS\system32 ... probably not
C:\WINDOWS ... probably not
c:\swipl\bin ... apparently yes as c:\swipl\bin\jpl.dll exists?
${env_var:PATH} ... apparently not
Try the suggestion from this question in your Java program:
File nativeFile = new File(filename + ".dll");
if (!nativeFile.exists())
System.exit(1);
System.load(nativeFile);
Note that just having jpl.jar is not enough. One needs the jpl.dll file, too. jpl.jar is good for the Java part of the Java-Prolog bridge, but to be able to call a non-JVM compilate, we need to get into system-level details, Hence the dll file.
See troubleshooting tips here: JPL Deploying for users - on Windows
From the above page:
If the Java examples complain that
The dynamic link library libpl.dll could not be found in the specified path
or
Exception in thread "main" java.lang.UnsatisfiedLinkError: C:\paul\bin\jpl.dll: Can't find dependent libraries
then there is no SWI-Prolog library libpl.dll in any folder on your
PATH: you should have a PATH entry such as C:\Program Files\pl\bin.
The libpl.dll should contain the code for SWI-Prolog itself.

Error: "UnsatisfedLinkError: com.aparapi.internal.jni.OPENCLJNI.getPlatforms()" JNI configuration

I would try to execute an example script based on Aparapi, on MAC OS. I'm using the last version of Eclipse, but when I execute DeviceInfo example to get all the available devices:
public class DeviceInfo {
public static void main(String[] args) {
KernelPreferences preferences = KernelManager.instance().getDefaultPreferences();
System.out.println("-- Devices in preferred order --");
for (Device device : preferences.getPreferredDevices(null)) {
System.out.println(device);
}
}
}
it generates the
java.lang.UnsatisfiedLinkError: com.amd.aparapi.OpenCLJNI.getPlatforms()Ljava/util/List"
Is there someone who can help me?

build the native assembly for Mac (x86_64) and add it into jniLibs; here's the source code.
java.lang.UnsatisfiedLinkError generally means, that it cannot find the native assembly.

Despite macOS Mojave 10.14.4 don't support directly OpenCL, I've executed Aparapi Framework.
I founded that the problem is the Aparapi Library. In particular, to resolve generated error I followed these steps:
Download this repository https://github.com/aparapi/aparapi for AMD Graphic Cards
Open the directory "com.amd.aparapi" and from terminal execute
ant -f build.xml
This command generates .jar file of this library
Add the generate jar to the project's classpath in Eclipse
Add the specific Aparapi library for your OS in:
<your-workspace-path>/<your-project>/src/main/resources/osx/
Before to execute the code, add the VM argument in "Run Configuration"
-Djava.library.path=<your-workspace-path>/<your-project>/src/main/resources/osx/
Execute your script!

can't run .jar file /java.jar: line 1: public: command not found

I have Ubuntu 16.04.
and downloaded a JDK with a tar.gz file extension and followed This wikihow to install it.
When I try to run a .jar game (like Minecraft) It works successfully, and I have netbeans downloaded that is connected to the same JDK and compiled some programs that i can run in terminal, But When I type :
./Hello_world.jar
Which is :
package main;
public class project {
public static void main(String[] args) {
System.out.println("Hello world");
}
}
I get this output :
./Hello_world.jar: line 1: $'PK\003\004': command not found
./Hello_world.jar: line 2: $'\b.\020oK': command not found
./Hello_world.jar: line 3: syntax error near unexpected token `)'
./Hello_world.jar: line 3:-oK�}����META-INF/MANIFEST.MFM�1
�0��#��uHh Q���X� ��N1�Ҧ$)��7�(�p�ww
�A����|��}�1���ή�n��p<�Рŗ��:CpN~�s�ν�˚�3��%
��)���goPK`

Simple: JAR files aren't executables. You can only invoke binaries/scripts by telling your shell to ./command.
They are archives that contain compiled Java classes.
Thus you use them like:
java -jar somejar.jar
This starts a java virtual machine, and tells it to open the given JAR file. The JVM will then figure the "main" class to run from the meta information that can be backed into the JAR file - to then "run" that main class.
( assuming that the corresponding JAR file has been built in a why that allows running it like this. see here for details on how you enable this "easy way" of running a JAR file )
And just in case: with some scripting magic, you actually can turn a JAR file into a "binary", see here for example.

Loading native libraries in java

I have an eclipse project with two classes. The class "SomeClass1" has a native method:
SomeClass1
public class SomeClass1 {
static {
System.loadLibrary("libname"); // Load the native library.
}
public native void some_method(); // implemented in the library
// .... other non methods ....
}
The other class "SomeClass2" uses the native method of "SomeClass1". Like:
SomeClass2
public class SomeClass2{
public static void main(String[] args) {
SomeClass1 s = new SomeClass1();
s.some_method();
}
// ....other methods....
}
However when it calls that method it throws an error like this:
Exception in thread "main" java.lang.UnsatisfiedLinkError: no libname in java.library.path
....
at java.lang.System.loadLibrary(Unknown Source)
at x.x.x.SomeClass1.<clinit>(SomeClass1.java:128)
at SomeClass2.main(SomeClass2.java:10)
I think the error has something to do with java not knowing where to look for the native library.
Question1
When I use: -Djava.library.path="C:\Users.....\libfolder\" as run argument in eclipse and print the value of: System.getProperty("java.library.path"); I see alot of directories printed but not the directory that I specified in the argument. What am I doing wrong?
Question2
When I do: System.loadLibrary("name"); do I need to call the library "name.so" or "libname.so"?
Question3
If the library would be found but was a 64 bit library while the platform it is loaded on is 32 bit, would it also give a unsatisfiedLinkError or would a different error be given?
Question4
Can I specify the path to the library relative to the projects folder or relative to the file in which the library is loaded?
Hope you are able to answer (some of) my questions.
Grtz Stefan

Question 1:
You should not add this as a run argument, but as a VM argument. It's not an argument for your program, but for the JVM.
Question 2:
(Also #IanRoberts ) : The System.loadLibrary(name) call will automatically derive the name of the actual library from the given name. That means that it will append ".dll" on windows, and use "lib" + name + ".so" on linux. Otherwise, loading a native lib would not be possible in a platform-independent way!
Question 3:
In general, the UnsatsfiedLinkError is distressingly common. It's in fact true to say: The UnsatisfiedLinkError does not tell you more than "Something is wrong". You can only hope for the actual error message to be more descriptive, and this would (fortunately) be the case if you had a 32/64bit mismatch - at least on windows:
Trying to load a 32bit lib on a 64bit system will cause the message: "Can't load IA 32-bit .dll on a AMD 64-bit platform"
Trying to load a 64bit lib on a 32bit system will cause the message: "... is not a valid Win32 application"
(I'm not sure about the message for other operating systems, though, but your message indicates that the library is just not found, and not that there's a problem with the library itself)
(Question 4: I'm rather sure that this is possible, but not absolutely sure (and can't try it out) at the moment. In general, the library must be in a path that is visible via the PATH environment variable, or via the java.library.path. In doubt, it should always work then the native libs are in the same directory as where you are starting your program from)

Java virtual machine launch issue

HI All,
I got an issue, all of a sudden Java stopped working completely. I start getting error like "Could not create the virtual machine". There is no issue with the memory (it has 3GB RAM) and was working fine for over a 6 months in this system without any issue.
Here are some peculiar behaviors -
When I start eclipse I see Java virtual machine dialog box with error messages like
"Could not find main class org.eclipse......support.legacysystemproperties"
Eclipse is able to start(with above error), but while running the program, I get error like "Could not create Java Virtual Machine" in a dialog box and after I click OK on that dialog box, I see error like "unrecognized option -dfile.encoding=cp1252
I used text editor, wrote a class Test.java (without any package), compiled it (Edit #1:javac Test.java). But when I execute the program (Edit #1:java Test), I get the following error -
Exception in thread "main" java.lang.NoClassDefFoundError: test (wrong name: Test).
Edit #1:
Note : The compiled file, Test.class is successfully created in the directory. I did recheck the path and classpath environment variables. All seem to be correct.
Please note that there seems to be some issues with cases which affected the Java.
I did uninstall Java (all versions), re-installed, but nothing helped. Also, I did run CCleaner to clean registry, Malwarebytes' Anti-Malware, but none helped so far.
Appreciate if someone could help me to resolve the issue.
I did googled for this and found that some have experienced similar issues, but none of them have found solution yet other than some suggestion that re-installation of Windows OS itself, which I want to avoid it. I did system restore, but that failed for some other
reason.
Please note that am using Java for over 10 years. This is first time am having such issue. This is something to do with Windows Registry or some other system configuration, but I am not able to find out the exact problem.
Anyways awaiting some good suggestion.

EDIT: Okay, so it looks like the Java executable is getting the command line arguments lower-cased.
Step 1: Verify
You can double-check whether this affects all command line arguments by creating a class with a lower-case name which just dumps its arguments:
public class test {
public static void main(String[] args) {
for (String arg : args) {
System.out.println(arg);
}
}
}
Compile and run this with a variety of inputs.
Step 2: Check scope
Assuming step 1 confirms the problem, if you've got .NET installed you can see whether it affects that as well. Create a file Test.cs:
using System;
class Test
{
static void Main(string[] args)
{
foreach (string arg in args)
{
Console.WriteLine(arg);
}
}
}
Compile this with "csc Test.cs" having found csc in the .NET framework directory (e.g. in c:\Windows\Microsoft.NET\Framework\v4.0.30319 for .NET 4).
Run it like this:
Test foo BAR Baz
and see what happens
Step 3: If step 2 showed that the issue is limited to java.exe:
Check your path, and work out where you're actually running java.exe from
Try explicitly running java.exe from your JRE or JDK directory