Develop Reference

Error when running Java file through Intellij terminal

In Intellij IDEA, when I run a java file in the terminal or run a jar artifact, I get this error:
I have an up to date jdk and runtime enviroment installed on my computer, and I only have one runtime environment installed. Also, I do not have an issue with the actual compilation of the program, just the
"$java Program" command.

The error message is clear: You compiled the Java source with an newer Java version than your are using to execute it.
So your assumption that you have only one Java version installed cannot be correct. Are you aware that the IDE itself comes with a Java runtime?
Next time please post text as text, not a link to an image.

java 1.8 jar runs in Windows not Ubuntu, "could not find or load main class ..."

I have a jar file that runs fine from the Windows 10 command line, but is not working on my desktop Ubuntu 18.04 command line. The file was exported from Eclipse as a jar, and copied to Ubuntu. The project has about 30 classes over a half dozen packages. I've done some renaming in order to simplify things for this question.
This is the command used to run the jar:
java -jar myproject.jar
On Ubuntu, I get the error "Could not find or load main class com.a.b.LaunchThis"
Following are some of the things I've tried, based on suggestions from many similar posts. Sorry if this is a duplicate, but I couldn't find a workable answer.
I verified that the current Java is 1.8 using the commands:
$ update-alternatives --config java
and
$ java -version
openjdk version "1.8.0_252"
OpenJDK Runtime Environment (build 1.8.0_252-8u252-b09-1~18.04-b09)
OpenJDK 64-Bit Server VM (build 25.252-b09, mixed mode)
(I also verified that the program runs using java 8 on Windows.)
I ran the following check, which displays all the files, and confirmed that com/a/b/LaunchThis.class exists and is spelled exactly the same way.
java tj myproject.jar
The manifest seems correct.
Manifest-Version: 1.0
Main-Class: com.a.b.LaunchThis
I also tried unpacking the jar and running the program directly from the folder /myproject which contains both /com and META-INF. That should work, shouldn't it?
java com.a.b.LaunchThis
java com/a/b/LaunchThis
java com.a.b/LaunchThis
And from one level outside the myproject folder:
java myproject/com/a/b/LaunchThis
java myproject.com.a.b/LaunchThis
java myproject.com.a.b.LaunchThis
java myproject/com.a.b.LaunchThis
I am not totally clear on when the syntax requires . or /. The package command in "LaunchThis" which holds the main entry point is the following:
package com.a.b;
And in each of the above iterations I also tried including "-cp myproject.jar" as an option.
Always the exact same error message.
To be careful about not having a typo in the above, I first ran the ls command to make sure the file could be found (then edited this line to create the variants).
ls myproject.com.a.b.LaunchThis.class
Any suggestions as to what else to try?
For grins, running with Java11 gets this response:
Error: Could not find or load main class com.a.b.LaunchThis
Caused by: java.lang.NoClassDefFoundError: javafx/event/EventHandler
This makes some sense, because Java11 does not include JavaFX. But Java 8 does include EventHandler. It's been a part of Java since JavaFX 2.
UPDATE: I made two "Hello world" jars, one with and one without JavaFX on an Ubuntu installation of Eclipse running OpenJDK 8. To get the version with JavaFX to run, I downloaded the Oracle JDK 1.8, and linked to /lib/etc/jfxrt.jar as an "external jar" library. Both programs run in Eclipse but only the non-FX jar works. The FX jar gives exactly the same error message.
I think this pretty much establishes my problem to be one of not having JavaFX as part of OpenJDK 8.
My plan is to now try out two solutions: (1) copying the Oracle jfxrt.jar into the OpenJDK lib, (2) backloading OpenJFX 8.
Simply installing OpenJFX from repository loads OpenJFX 11, which is a little dated but will work with the OpenJDK 11.

The issue here is that the repository OpenJDK 8 on Ubuntu 18.04 does not include JavaFX. I'm guessing that the error message results from the fact that a JavaFX main() is located on a class that extends the JavaFX class Application.
How to fix this?
There are a number of things I tested.
First, one could use Oracle's JDK 1.8 instead. I ruled this out due to licensing issues.
Some sites suggested copying the jfxrt.jar from either the Oracle JDK 1.8 or from a working Java program that uses JavaFX and uses a self-contained JRE. I found that if I linked to the Oracle jfxrt.jar (located in the /jre/lib/ext folder) as an external jar, I could run a simple, "Hello world" javafx program in Eclipse. But I could not run the program after it was exported to a jar.
One answer on a related stackoverflow thread suggested copying over several additional files along with jfxrt.jar, which I tried. This did not work, so I'm not going to pass that on.
The solution that has been most successful came from a link provided in the comment by #dave_thomson_085, How do I get Java FX running with OpenJDK 8 on Ubuntu 18.04.2 LTS?.
This answer involves purging and reinstalling openjfx with an older version, and marking it to NOT be subjected to updates.
The code provided by Wolfgang Fahl (which he credits to Druidefix) follows:
apt purge openjfx
apt install openjfx=8u161-b12-1ubuntu2 libopenjfx-jni=8u161-b12-1ubuntu2 libopenjfx-java=8u161-b12-1ubuntu2
apt-mark hold openjfx libopenjfx-jni libopenjfx-java
Now, I can run and test jars containing Java8 using JavaFX that were built on my Windows Eclipse, on my Ubuntu desktop.
I do get a warning message which I haven't dealt with yet:
Gtk-Message: 13:25:40.829: Failed to load module "canberra-gtk-module"
But this is not preventing my programs from running.

Unable to run Stand alone Java Swing application in different machines

I have created a Java Swing application in eclipse. And I have packaged the application into Runnable JAR with the help of Eclipse Export functionality. But I am unable to run the JAR in other machines. In my system it is working fine.
How to make it independent?
The default output folder(i.e for class files) : Project_Name/bin
The JRE is present in the C:/Programfiles/java/jre7
I have a sqljdbc Jar which is placed in the lib folder of the Project in my D drive.
I am using the option "Package Required libraries into generated JAR" but still I think the JAR is not able to fine the correct libraries when I am double clicking on teh JAR in a different machine.
Please suggest. Thanks for all your help.

I am getting UnsupportedClassVersionError in the cmd when I am trying to run the JAR through cmd in other machines
This means that you are using a lower version of the JRE than the JDK which you used to compile the sources (for example, sources compiled with JDK7 can not be executed by a Java 6 or lower JRE since the class file format and hence the class version has changed).
I am also getting unsupported major.minor version 51.0
51.0 is the class file version of JDK 7. Again, this indicates that you try to run your code with Java version 6 or lower.
To verify, check with
C:> java -version
which java version is actually used by default.
To fix this issue, use an absolute path to the java version you require, like
C:> C:\Programfiles\java\jre7\bin\java -jar myapplication.jar

Having troubles compiling Java programs

Sorry I couldn't be more specific with the question itself. Here's what I'm running: Windows 7 64bit, JDK v7, JRE v7 (64 bit), and JRE v6 (32 bit). I'm pretty new when it comes to Java, however I do know how to compile a program and all that stuff. I kept getting an error when I tried running my compiled programs:
C:\Users\Sean\Documents\JAVASTUFF\Chapter 3\1>javac ch3p1.java
C:\Users\Sean\Documents\JAVASTUFF\Chapter 3\1>java ch3p1
Error: could not open `C:\Program Files (x86)\Java\jre6\lib\i386\jvm.c
C:\Users\Sean\Documents\JAVASTUFF\Chapter 3\1>java -cp ch3p1
Error: could not open `C:\Program Files (x86)\Java\jre6\lib\i386\jvm.c
C:\Users\Sean\Documents\JAVASTUFF\Chapter 3\1>java cd3p1
Exception in thread "main" java.lang.NoClassDefFoundError: cd3p1
Caused by: java.lang.ClassNotFoundException: cd3p1
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
Could not find the main class: cd3p1. Program will exit.
C:\Users\Sean\Documents\JAVASTUFF\Chapter 3\1>java -version
java version "1.6.0_29"
Java(TM) SE Runtime Environment (build 1.6.0_29-b11)
Java HotSpot(TM) Client VM (build 20.4-b02, mixed mode, sharing)
note that it couldn't find the file because I had changed the folder name to see if it would automatically detect the 64 bit JRE I have installed
However, after enough searching I found a page that stated my problems were because I was running a program I compiled on JDK v7 in JREv6. I messed around with that for a little while, trying to get it to run in the JRE that came with my download of JDK.
CD: C:\Users\Sean\Documents\JAVASTUFF\Chapter 3\1
Current directory: C:\Users\Sean\Documents\JAVASTUFF\Chapter 3\1
javac ch3p1.java
Process started >>>
<<< Process finished.
C:\Program Files\Java\jre7\bin\java.exe ch3p1
Process started >>>
Error: Could not find or load main class ch3p1
<<< Process finished.
I'm using Notepad++ and NppExec to compile faster, and I gave up trying to get it to run JRE v7 and just used the location of it. And here's my NppExec code (I don't know if it's important, but I'll post it anyways):
cd $(CURRENT_DIRECTORY)
javac $(FILE_NAME)
C:\Program Files\Java\jre7\bin\java.exe $(NAME_PART)
And, finally, here's the actual program I'm trying to get to run:
public class ch3p1
{
public static void main(String args[])
{
System.out.print("Hello.");
}
}
So, a quick recap. The first error I found out was because I was compiling and running a program with different versions of JDK and JRE. I couldn't figure out how to actually make it run with the JRE that came with my JDK installation so I used the direct path to it instead. My hopes got crushed that this would work when I went to run my compiled program. I got a simple "Error: Could not find or load main class ch3p1".
What's the question? I don't know exactly, the broad question is: What do I need to do to get this to work? I cannot be any more descriptive than that because I have no idea what to do or where to look next. I'm hoping I provided enough useful information and structured it well enough to make it comprehensible.
Some other questions: Will removing the two Java 6 updates in my Add/Remove Programs work? How do I change it so whenever it runs java, it'll run the 64bit JRE v7?
I have no idea what I'm doing here and I'm basically learning as I go. I am familiar with computers to an extent but I am new to Java and JDK so I don't know much about how it works. My leads might be completely misdirected and wrong, if so, please correct me.
EDIT
I understand that there are a lot of questions on this website and I'm sure the people posting here answer a lot of questions that can be solved with minimal to no effort involved. I have to say that I have looked everywhere and I came here to post this because I simply cannot find the solution to my problem. I wasn't looking for help on finding another program to use, and I definitely was not putting the files in my Java installation directory because despite me being new to Java, I am not new to programming. That response could have been easily avoided by looking at the first example I provided, and another one where the file path to my .java and .class files can be seen in a folder in my Documents.
I will list answers and what I have tried here:
I reinstalled JDK and JRE from the Oracle website
I have set my SET_HOME system variable and my Path system variable has the JDK bin directory in it.
My .class file and my .java file are in the same directory, and my class and the .java file are both named the same thing, including exact cases.
After I installed JDK and JRE I deleted my previous files and made a new one, and that didn't work either.
I tried putting the direct locations of java and javac as suggested in a reply.
I realize that there are better IDE and build programs out there, I am using javac because the class I am in right now is using javac.
Now, for some extra questions to help me out:
I have the Java v6.xx updates in my add/remove programs list, would removing these in any way effect anything in a positive or negative way. And would complete removal of all JDK/JRE files and re-installation change anything?
Is there any known issues with using Java and Windows 7 that I might be running into.
Is this an issue with JRE or JDK, because it seems to be compiling without any issues but when I go to run it is when I get the errors.
Are there any other variables other than CLASS_PATH or Path that I need to set?
I appreciate any and all help that's been given so far even though I haven't found a solution yet.

Try using the absolute path to the directory where you installed java. Here is what I would type on my machine
cd "C:\Users\Sean\Documents\JAVASTUFF\Chapter 3\1"
"C:\Program Files\Java\jdk1.7.0_02\bin\javac" ch3p1.java
"C:\Program Files\Java\jdk1.7.0_02\bin\java" ch3p1
if that works, you should add the directory to the path so that this is the preffered java version. This way you won't have to use the absolute path anymore and just type "java" and "javac" as usual
set PATH="C:\Program Files\Java\jdk1.7.0_02\bin\";%PATH%
Setting the path can also be done somewhere in the Control Panel so that you don't have to type that in each time you open a command prompt
Edit: You should probably set JAVA_HOME as well as "duffymo" suggests. If it still doesnt work there may be something wrong with your java installation. Try downloading and installing a new version from Oracle

Let's start by saying you should never, ever put any of your code in the directories where you installed Java JDK. Please make it a habit to create a separate folder (e.g. "c:\work") and put your project sub-folders there.
Open a command shell and type this: java -version. That will tell you the version of Java you're compiling and running with. You care about the JDK, because you're developing code.
Is your JAVA_HOME environment variable set? Please point it to the directory where you installed Java. Then add %JAVA_HOME%\bin to your PATH. If you do all this correctly, you should be able to compile in a command shell by typing javac.
So, create a folder c:\work\learning\src and put your ch3p1.java folder in it. Create a directory c:\work\learning\classes, too. Compile your code with this command:
javac -cp .;classes -d classes src\*.java
You should see ch3p1.class in the classes folder.
Run it with this command:
java -cp .;classes ch3p1
You'll see "Hello." in the console.
EDIT: I'd recommend that you read this tutorial carefully:
http://docs.oracle.com/javase/tutorial/getStarted/cupojava/win32.html
You aren't the first person to compile and run "hello world". It seems to me that you're thrashing around too much. Simplify.

Several things here.
Java compiler can take a "target" argument to indicate for which Java version you wish to compile. By default, the target is the version of the current JVM.
So far, any class compiled with a given target is compatible with that target and any above version. So a class compiled for Java 5 is compatible with Java 5, 6 and 7.
To find out which version of Java you are running, type java -version in your terminal. It will output something like "Java 1.X..." The 'X' is the version of Java and you will often see people talking about Java 5 or Java 1.5 which is the same thing (same goes for 6 and 7).
The version that is running depends on several parameters, but usually it all comes down to the first Java bin directory in your 'PATH' environment variable.
Now, if you are considering Java IDE, there are 3 major ones:
Eclipse
NetBeans
IntelliJ
All three are fine Java IDE's and it is pretty much religious which one you will prefer. Personnally I use Eclipse.
Finally, for you problem:
Comiple using javac ch3p1.java
Run using java -cp . ch3p1

Include Swing when compiling with javac

I compile and jar the source just fine, but when I run it, it complains:
java.lang.ClassNotFoundException: javax.swing.JPanel
I guess I have to include the Swing library when compiling, but how do I do that?
I included every rt.jar on my system:
javac -classpath /usr/lib/jvm/java-1.5.0-gcj-4.4/jre/lib/rt.jar:/usr/lib/jvm/java-6-sun-1.6.0.20/jre/lib/rt.jar:/usr/lib/jvm/java-6-openjdk/jre/lib/rt.jar:/home/me/equinox.jar *java
Still compiles fine, still crashes when run.

It looks like you are using GCJ. It's an old project that attempted to produce a Java implementation as pure open source.
They got about halfway, but the implementation is far from perfect. These days, it's better to avoid it entirely and instead use OpenJDK (or the Oracle/Sun JDK, if open source is not a requirement).
On Ubuntu you can use update-java-alternatives to configure your system to a different Java implementation:
sudo update-java-alternatives -s java-6-openjdk
By the way, you never need to specify rt.jar explicitly on your classpath, as it's always available automatically. Also, using multiple rt.jar from different JVMs is a recipe for disaster.

If you run the code, the compilation worked fine.
It is weird that you are missing this particular class as it is part of the standard library. In most Java distributions, this is in rt.jar

What is your current path to the JDK (in $PATH or %PATH%)? What is your whole path? What is your current CLASSPATH environment variable? Your problem is runtime environment related. You should not add rt.jar to your classpath. If you have a proper JVM install, then java doesn't need the location to rt.jar and tools.jar. I suspect that you have pathing issues to the JVM.
Also, what is the command line you are using to run the program?

You don't need to include rt.jar, it is included by the default classloader of the java vm.
You need to find out which version of java is the default one:
java --version
if you're running ubuntu, it will most probably be openjdk java, which is fine. If it's gcj, try to run it with openjdk or sun-jdk.
Also, show exactly how you run the jar.