I have a single .java (driver.java) file I'm trying to compile and run from the command-line. It uses the external library called EXT.jar, whose structure is just a folder called EXT with a few dozen classes within it.
So I run:
javac -cp EXT.jar driver.java
This compiles the class just fine.
then when I run:
java -cp EXT.jar driver
I get a java.lang.NoClassDefFoundError.
Oddly enough, if I unpack the JAR (so now I have a folder in the root directory called EXT), the last command works just fine!! Driver will execute!
Is there any way I can make the driver.class look for the need class files from EXT.jar/EXT/*class instead of an actual EXT folder?
Thanks!
You're compiling the class to the local directory. So when you run it, you need to include the current directory in your classpath. E.g.:
java -cp .;EXT.jar driver
Or in linux:
java -cp .:EXT.jar driver
With the way you have it now, you're saying your classpath is only EXT.jar (along with whatever is in the CLASSPATH environment variable) and nothing else (which is why the current directory, where driver.class is located, is excluded)
Related
I'm on Ubuntu 22.04 trying to run my code in the terminal.
The program works without problems in VScode, also when running multiple instances.
The program is consisted of six class files.
The trouble occurs when I try and run it with terminal. When compiling the java file
with javac it shows errors at places where I use the external libraries.
If I compile it with VScode and run the class file in terminal, I get the following error java.lang.ClassNotFoundException
This is causing me problems since I'm also supposed to dockerize the program.
You can add the following code in your setting.json file "java.project.outputPath": "bin",
This will be the .class file generated by VS Code in the bin folder of the same directory when running the Java code.
You can use the java command after entering the file directory with the cd command.
This generally indicates that the class path with which you're compiling your program does not include the correct paths to your libraries. Assuming your libraries are jar files, your javac command should look something like this:
javac -cp libs/lib1.jar:libs/lib2.jar srcs/*.java
where libs/ is the relative path to your libraries and srcs/ is the relative path to your own java files.
And when you run the program, make sure your class path includes both the locations of your libraries and the location of your class files (which in this case would be the current directory):
java -cp .:libs/lib1.jar:libs/lib2.jar <MainClass>
After I build this project from an ant file, I recieve a jar that contains all of the classes I built. When I try to run this jar, I get the following error:
Exception in thread "main" java.lang.NoClassDefFoundError: javax/media/j3d/SceneGraphObject
This error indicates that a one of the jars, specifically the j3dcore.jar from java3d, I am using can not be found. However, this jar is on the classpath when compiling through the ant build into the class files.
Why can this class not be found at runtime, but it is found at compile time? Do I have to manually change my classpath in my shell when running the jar as well as change it in the ant build?
If I add the jars to my classpath using java -cp j3d/*.jar -jar idv.jar
I get the error Error: Could not find or load main class j3d.j3dutils.jar
Do I have to manually change my classpath in my shell when running the jar as well as change it in the ant build?
Yes, absolutely. Making a class available at compile-time doesn't embed the class into your output or anything like that. It just makes it available to the compiler (to find out what methods are present etc).
If I add the jars to my classpath using java -cp j3d/*.jar -jar idv.jar
Yes, it would - because that's being expanded into:
java -cp j3d/foo.jar j3d/bar.jar ... -jar idv.jar
It's not clear to me whether -cp is meant to work at all with -jar, given this documentation:
When you use this option, the JAR file is the source of all user classes, and other user class path settings are ignored.
One option is to set the classpath within the manifest of the jar file itself. For example:
Class-Path: j3d/foo.jar j3d/bar.jar
Another would be to ignore the -jar command-line option for now, and use:
java -cp j3d/*:idv.jar your.class.name.Here
Note the * rather than *.jar, as documented:
As a special convenience, a class path element containing a basename of * is considered equivalent to specifying a list of all the files in the directory with the extension .jar or .JAR (a java program cannot tell the difference between the two invocations).
I've been learning about JAR files and wanted to try and create and run one myself. I carried out the following steps:
Created a project folder with a 'source' subfolder and a 'classes' subfolder
I wrote 2 source files, one with a main method which creates an instance of the other class and runs a simple method in it.
Compiled these to the 'classes' subfolder. I checked to see if they would run. They did
I created a manifest.txt file and filled in the Main-Class: xxxx and hit the return key. I saved this in the sources subfolder
Created a jar file in the classes subfolder by writing
jar -cvmf manifest.txt zzz.jar *.class
Tried to execute the jar file by typing
java -jar zzz.jar
This gives a ClassNotFound exception. If I try to execute the jar by double clicking on it in windows I get an errorbox saying "Could not find the main class xxxx"
I've double checked the spelling of the class inside the manifest file and it's correct.
Possibly important: I have to compile my programs using java -cp . xyz as there is an issue with my classpath. Does this mean that I need to execute jars in a different way as well? I tried
java -cp . -jar zzz.jar
but ended up with the same exception.
Edit: I ended up starting from scratch and now it runs (with the basic -jar zzz.jar command). Frustrating that I don't know what I was doing wrong but glad that it is working!
Shouldn't number 5. be run in the classes subfolder, where all your class files are? And if your classes are in packages, which they should be, you'll likely want to use * instead of *.class..?
To check what your jar file contains you can run:
jar tf zzz.jar
You will probably have to supply the entire path of the .class file you wish to execute after the classpath. ie java -cp xxx.jar classes.mainProgram.class. Where classes is the name of the folder which contains your class files.
I am trying to run a jar file using my command prompt (Windows XP) but get NoClassDefFoundError.
I have my DateAndTime.class file in a folder called dateandtime and also indicated a package called dateandtime in the source file.
Outside the folder I have a manifest.mf file with specification
Main-Class: dateandtime.DateAndTime
I put this in the command file
jar cmf manifest.mf myJarFile.jar dateandtime
and this creates the myJarFile.jar in the same folder as manifest.mf.
When I try to run this jar file however I get the NoClassDefFoundError
java -jar myJarFile.jar
If I jave all the classes in the same directory with no package specified then the .jar file runs fine but as soon as I try to specify a package, even though myJarFile.jar was created I get the error.
Why is that?
Regards
If you are getting a NoClassDefFoundError it means a class that was present during compilation of your classes is absent during their execution. Which implies that you JAR file does not contain all the dependencies requires by your classes in order to run. Since your question is lacking detail on your project structure I can only recommend you revisit your application's dependency tree and determine all the classes that need to be included in the JAR.
Syntax:
java -jar fileName.jar
Example:
java -jar myfile.jar
With reference to this post
Receiving "wrong name" NoClassDefFoundError when executing a Java program from the command-line
I did not understand how to solve the problem
Actually in my java source code there' s line :
package es_2011;
when I compile the program through JCreator everything works perfectly.
It creates a folder named es_2011 where to put .class files.
Also the executing operation goes smoothly, the program runs ok.
Now I'd like to use the command line only.
So I placed my java file in the directory where javac.exe is but whenever I try to compile I get the same error
The command I use is: javac ProgAudioJ.java
The path (where javac.exe is ) is : C:\Program files\Java\jdk1.6.0_22\bin
Is someone willing to help me understand in terms of exactly tell me what I have to do?
thanks very much...MAX
The setup used for the looks like this (under windows)
C:\classDir -> is the project
C:\classDir\testpackage -> is the only package used (the package "testpackage")
C:\classDir\testpackage\Main.class -> is the class with the main method inside (important: it is the .class and not .java)
The Main.class looks like following:
package testpackage;
public class Main {
public static void main(String[] args) {
System.out.println("Program started! ;-)");
}
}
go with your command prompt to:
c:\classDir> java testpackage.Main
the result:
Program started! ;-)
According to your problems that it starts in your IDE but not from the console:
- checked if you realy use the path to the .class files?
- with the console go to the directory of you .class files, not the project (e.g. in Eclipse it is the bin directory
- enter the full qualified class name (including packages seperated by . -> e.g. testpackage.Main
More infos can be found under:
http://www.oracle.com/technetwork/java/compile-136656.html
Hope it helped
MAX, if the class defines that it's inside the package es_2011, then it should be in a folder with the same name.
So in your case, put the ProgAudioJ.java in the folder es_2011 and then run
javac es_2011\ProgAudioJ.java
latter to run it, you need the command
java es_2011.ProgAudioJ
You should add javac.exe in your path .Edit your path variable and append path to jdk's bin
then put java file in a dir named es_2011 , as the package declaration is es_2011 then compile
c:\es_2011\javac YourJava.java
and now go back to C:
c:\java es_2001.Yourjava
After reading you other Post: "Receiving "wrong name" NoClassDefFoundError when executing a Java program from the command-line" I guess you go to the directory es_2011 where your ProgAudioJ.class file is located and run
java ProgAudioJ
from that folder.
instaend you have to go to the folder above (cd ..) and run
java es_2011.ProgAudioJ
Each package in Java corresponds to a folder on the filesystem. So a package declaration such as com.stackoverflow would mean that the source classes need to be in a folder ./com/stackoverflow. Typically the whole project would have a separate src folder containing com/stackoverflow.
When you compile the Java classes you DO NOT need to put source files in the same directory as javac.exe, you do however need to make sure that javac.exe is in your operating systems PATH variable. This tells the operating system where it should look for executable files when a command is run, on a *nix machine this would usually be /usr/bin or just /bin but on Windows machine the executables normally live within the applications own directories, that is C:\Program Files\something. Assuming that you've installed JDK correctly, the javac.exe should already be in the PATH you can check this by opening the command line and just running javac (just like that). If you get some output then all is well, the system knows where to find javac.exe.
Next you will need to go to your project folder and type javac -d . src/com/stackoverflow/MainSO.java notice that is run from the project folder. This will create a folder called com in your project root and put the compiled classes in com/stackoverflow. The -d flag tells javac where to put the compiled classes, if you leave that out, the compiled classes will be where the sources are.
Then when you want to run the classes you type java com.stackoverflow.MainSO (no .class). Crucially this command will need to be ran in the directory that contains the root of the class hierarchy (that is the com folder containing the compiled classes). You can specify other places for java to look for the classes by providing a classpath to the java command with the -cp flag. By default the classpath will contain the directory the java command was ran in. Should your project have dependencies external .jar files for example you will need to provide every single one of them (with their full filepath) in the classpath (this goes for the compiler as well). The IDEs do this automatically for you.
Hope that helps.