I am trying to run a Java application, but getting this error:
java.lang.ClassNotFoundException:
After the colon comes the location of the class that is missing. However, I know that that location does not exist since the class is located elsewhere. How can I update the path of that class? Does it have something to do with the class path?
A classpath is a list of locations to load classes from.
These 'locations' can either be directories, or jar files.
For directories, the JVM will follow an expected pattern for loading a class. If I have the directory C:/myproject/classes in my classpath, and I attempt to load a class com.mycompany.Foo, it will look under the classes directory for a directory called com, then under that a directory called mycompany, and finally it will look for a file called Foo.class in that directory.
In the second instance, for jar files, it will search the jar file for that class. A jar file is in reality just a zipped collection of directories like the above. If you unzip a jar file, you'll get a bunch of directories and class files following the pattern above.
So the JVM traverses a classpath from start to finish looking for the definition of the class when it attempts to load the class definition. For example, in the classpath :
C:/myproject/classes;C:/myproject/lib/stuff.jar;C:/myproject/lib/otherstuff.jar
The JVM will attempt to look in the directory classes first, then in stuff.jar and finally in otherstuff.jar.
When you get a ClassNotFoundException, it means the JVM has traversed the entire classpath and not found the class you've attempted to reference. The solution, as so often in the Java world, is to check your classpath.
You define a classpath on the command line by saying java -cp and then your classpath. In an IDE such as Eclipse, you'll have a menu option to specify your classpath.
Your classpath is broken (which is a very common problem in the Java world).
Depending on how you start your application, you need to revise the argument to -cp, your Class-Path entry in MANIFEST.MF or your disk layout.
This is the best solution I found so far.
Suppose we have a package called org.mypackage containing the classes:
HelloWorld (main class)
SupportClass
UtilClass
and the files defining this package are stored physically under the directory D:\myprogram (on Windows) or /home/user/myprogram (on Linux).
The file structure will look like this:
When we invoke Java, we specify the name of the application to run: org.mypackage.HelloWorld. However we must also tell Java where to look for the files and directories defining our package. So to launch the program, we have to use the following command:
NOTE: You have to execute the above java command no matter what your current location is. But this is not the case for javac. For
compiling you can even directly go into the directory where you have
your .java files and directly execute javac ClassName.java.
If you know the path of the class or the jar containing the class then add it to your classpath while running it. You can use the classpath as mentioned here:
on Windows
java -classpath .;yourjar.jar YourMainClass
on UNIX/Linux
java -classpath .:yourjar.jar YourMainClass
I had the same error and it took me a whole day to realize it's a dependency conflict issue:
I imported two libraries, A and B;
Both A and B depends on another library C, but different versions of C. Let's say A depends on C 1.0 and B depends on C 2.0;
B makes use of a class that only exists in C 2.0;
However, A is "closer" in the dependency tree, so Maven uses C 1.0 for both A and B and doesn't even warn you about this (it's quite astounding to me);
As a result, when B tries to use the class that only exists in C 2.0, a ClassNotFoundException is thrown;
Now the weird thing is: if you navigate the code of B in your IDE and try to jump to the class that only exists in C 2.0, it works correctly. C 2.0 is indeed installed and your IDE knows about it, but it's just ignored when running the application.
This really drove me mad...
I ended up having to add C 2.0 to my pom.xml so that it can be chosen over C 1.0.
Please refer to this post for how Maven chooses the closest dependency: https://stackoverflow.com/a/63815140/7438905
You can use mvn dependency:tree to visualize the dependency tree.
Try these if you use maven. I use maven for my project and when I do mvn clean install and try to run a program it throws the exception. So, I clean the project and run it again and it works for me.
I use eclipse IDE.
For Class Not Found Exception when running Junit test, try running mvn clean test once. It will compile all the test classes.
Basic Generic Question - Simplest Generic Answer ;)
Given the information I will make the assumption that you might be trying a basic approach to coding, building/compiling and running a simple console app like "Hello World", using some simple text editor and some Command Shell.
This error occurs in the fallowing scenario:
..\SomePath>javac HelloWorld.java
..\SomePath>java HelloWorld.class
In other words, use:
..\SomePath>java HelloWorld
P.S. The adding the file extension .class produces the same mistake.
Also be sure to have the Java's (JDK/JRE) bin folder in the operating system's Environment Variables's PATH.(Lookup for more details other posts on this)
P.P.S Was I correct in my assumption/s?
If you use maven, check that you have this plugin in your pom.xml:
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-shade-plugin</artifactId>
<version>3.2.0</version>
<executions>
<!-- Attach the shade goal into the package phase -->
<execution>
<phase>package</phase>
<goals>
<goal>shade</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>
It will put your dependency (the exception reason) to your jar.
FYI:
this will include all dependencies inflated in the final jar
To add the location of a class to your classpath via command line simply add -cp or -classpath and the location of the class while running it. I.E.
java -cp "c:/location/of/file" YourProgram
Or if you're running an IDE such as eclipse you can right click on the project -> build path -> configure build path
and add the external JAR containing your class to the build path then it should work fine.
Use ';' as the separator. If your environment variables are set correctly, you should see your settings. If your PATH and CLASSPATH is correct, windows should recognize those commands. You do NOT need to restart your computer when installing Java.
Add the full path of jar file to the CLASSPATH.
In linux use: export CLASSPATH=".:/full/path/to/file.jar:$CLASSPATH". Other way worked (without editing the CLASSPATH) was unzipping the jar in the current project folder.
Ways didn't work for me:
1) Using -cp option with full path of jar file.
2) Using -cpwith only the name of jar when located in the current folder
3) Copying the jar to the current project folder
4) Copying the jar to standard location of java jars (/usr/share/java)
This solution is reported for class com.mysql.jdbc.Driver in mysql-connector-java.5-*.jar, working on linux with OpenJDK version 1.7
This can happen on Windows after a java update where the old version of the java SDK is missing and a new one is present. I would check if your IDE is using the installed java SDK version (IntelliJ: CTRL + SHIFT + ALT + S)
Go up to the top and remove the import statement if there is one, and re import the class. But if that isn't the case do a clean then build. Are you using Netbeans or Eclipse?
I ran into this as well and tried all of the other solutions. I did not have the .class file in my HTML folder, I only had the .java file. Once I added the .class file the program worked fine.
It could happen if your classpath is not correct
Let us posit a serializable class and deserializable class under same projectname. You run the serializable class, creating a serializable object in specific folder. Now you need the desearialized data. In the meantime, if you change the name of the project it will not work. You have to run the serializable class first and then deserialize the file.
If you are using maven
try to maven update all projects and force for snapshots.
It will clean as well and rebuilt all classpath..
It solved my problem..
I just did
1.Invalidate caches and restart
2.Rebuilt my project which solved the problem
It's worth noting that sometimes Java lies about the Class that is causing the problem.
You can get this error if java tries to load class A which depends on class B and class B can't be loaded.
In some circumstances java reports that class A can't be loaded when the problem is B.
From recollection the last time this occurred was when class A includes a static field or a static initializer that loaded class B.
So after checking your class path is correct (I actually dump the full classpath on startup) I then do a binary chop on class A.
By this I mean, I remove half of the code in A.
If it still fails I remove another half and so on until the problem (hopefully goes away).
I was trying to run .jar from C# code using Process class. The java code ran successfully from eclipse but it doesn't from C# visual studio and even clicking directly on the jar file, it always stopped with ClassNotFoundException: exception. Solution for my, was export the java program as "Runnable JAR file" instead of "JAR File". Hope it can help someone.
If you have added multiple (Third-Party)**libraries and Extends **Application class
Then it might occur.
For that, you have to set multiDexEnabled true and replace your extended Application class with MultiDexApplication.
It will be solved.
In my case the class thrown as class not found exception has properties related to ssl certificates. Close the eclipse and open with as “Run as Administrator” then issue got resolved. As eclipse have issue related permission it will throw such kind of exception.
I started having this issue after upgrading the "Java Language Support" plugin from Visual Studio Code from version 0.66.0 to 0.67.0.
Downgrading back allowed me to run the same code without any issue.
If you have moved your project to new machine or importing it from git, then try this.
Right Click on class > Run as > Run Configuration
remove main class reference
Apply > Close
Now again right click on class > run as java application.
It worked for me.
I ran the Java code at the Terminal and adding Class Path was solution like this:
> java -cp <JAR file> <JAVA Class file>
for example,
c:\code\prototype-app\target\classes>java -cp ..\prototype-app-1.0-SNAPSHOT.jar com_stree.app.DetectLabels
My runtime environment:
OS: Windows 10
JAVA: 15.0.1
Maven: 3.8.1
Check the .jar or .class file permissions. I had the jar on a project library with permission of -rw-r--r-- and I changed it to -rw-rw-r-- using on Linux:
chmod 664 <.jar>
One library was calling ClassLoader.loadClass which started the error when loading the class in the jar with wrong permission.
I deleted some unused imports and it fixed the problem for me. You can't not find a Class if you never look for it in the first place.
sorry i am late to the question, but i will explain it to you in the simplest layman language.
When you type 'javac <programname.java>
The compiler checks the program and finds errors, first of all make sure your program is in the same directory as you have executed in the command prompt. Then it creates a. Class file of your program. For ex. If the name of my program was Test.java then the class file created should be Test.class which will be executed in the next line.
Sometimes java takes some other name for your .class, use that name and voila you'll get the output.
Put all the code in try block then catch exception in a catch block
try
{
// code
}
catch(ClassNotFoundException e1)
{
e1.getmessage();
}
I am making a 2d game, which I have compiled into a .jar to test if it works.
When in run the jar file with java -jar command I get the following error:
Error: Could not find or load main class com.grizeldi.splatoon.Main
I know that there are many solutions here on StackOveflow, but I have tried updating java, messing with -cp... Nothing worked so far.
Code: github repo
Help anyone?
EDIT1: I have my code on a USB stick, but I have tried moving it to C: and D: but nothing worked.
EDIT2: I have added the .jar on the github.
One way is to update the Manifest with the classpath to the other jars:
Class-Path: lib.jar
An alternative is to add the contents of the jars your main jar depends on to your main jar, so you have only one jar file. Make sure you don't add the jars themselves to the main jar, as nested jars won't work.
When dealing with native libraries (.so, .dll), simply place these in the same directory as the jar. The downside of this is that you have multiple files.
In that case, it might be easiest to just add a startup script (.sh, .bat), specifying the classpath and the classname of Main, aswell as a -Djava.library.path.
There is also another way: extract the native library from the jar at runtime, save it to a temporary location, and load it explicitly. See here for more info on that.
I am trying to run a java program through the Terminal on Mac, yet getting:
Error: Could not find or load main class (MY CLASSNAME)
I compiled this application with Eclipse, and when I run this with Eclipse, it works fine.
Furthermore, I am in the right directory, as when I type "ls" in the Terminal, it lists all the files, includes the class file I am trying to run.
This is what I type:
java mainClass
I would very much appreciate help to solve this!
Thank you,
Dean
EDIT: Solution - instead of java mainClass, it must have package too: java startPackage.mainClass
Start by making sure you are at the directory above the top level package
If the class belongs to the package com.foo.bar, you want to be in the directory above com.
In your case, you want to be in the directory above startPack.
Then you need to use the fully qualified name to run the class...
java statPack.mainClass
For example...
Make sure you have the current directory inside your CLASSPATH.
java -cp . mainClass
To set this globally, you can use export CLASSPATH=$CLASSPATH:. inside .bash_profile.
Separately, if your class lives inside a package such as com.foo.bar, then you will need to go to the parent directory of com and run your application with the full path.
java com.foo.bar.mainClass
I too faced this on Mac machine and then what I had to do to make it work was:
Problem Statement:
I had one package xyz under the root of project i.e src/main/java and then inside xyz package I had one class Student.java
my current directory is /Users/username/projectname/src/main/java/xyz:
I can see Student.java exists here
and I compiled it using javac Student.java
Now I see class file has been created at this location. But when I try to run the class file using java Student
I get the error: Error: Could not find or load main class Student
Solution:
Now the solution is to go one step back in the directory and go to root path:/Users/username/projectname/src/main/java and run the command
java xyz.Student
and it will work.
Link to follow: https://javarevisited.blogspot.com/2015/04/error-could-not-find-or-load-main-class-helloworld-java.html
For people dumb like me, make sure you are typing java HelloWorld - and NOT java HelloWorld.class - to run the compiled file with the name HelloWorld.class. This is especially so if you are used to hitting the tab key to complete the file name, as the terminal will give you java HelloWorld.class if you hit the tab key for autocomplete after typing something like java He...
This answer is here because it took 3 sites, including this answer, and 25 mintues before I figured out what I was doing wrong.
Logic is easy, typing is hard.
Using the absolute path can also resolve this problem:
java -classpath /Users/xingliu/IdeaProjects/springproject/src/main/java/ startPackage.mainClass
I'm grading an assignment in Java. Students are asked to implement a Five-In-A-Row (like Tic-Tac-Toe, or two-player Pente) interface which is used by a GUI .java file. These files (interface and GUI) are given to the students in a file called lab2.jar (where they're in cs251/lab2/ under the names GomokuModel and GomokuGUI, respectively), which the students must add to their classpaths. When the project is finished, students are requested to turn in a .java file called Gomoku.java.
One student turned in a .jar, but the command
java -jar Gomoku.jar
responds with
no main manifest attribute, in Gomoku.jar
I figure the student may have forgotten / not known to make a manifest file. I unzip the student's jar and find only .class files. I try to make my own jar from these files:
According to specs, the main must be in Gomoku.java, whose class is Gomoku.class. So I make a manifest.txt file that looks like
Main-Class: Gomoku
Class-Path: lab2.jar
And try to make a .jar out of it using the command
jar cfm myJar.jar manifest.txt *.class lab2.jar
But when I run this using the command
java -jar myJar.jar
I get the following error:
0Exception in thread "main" java.lang.IllegalAccessError: tried to access method cs251.lab2.GomokuGUI.<init>(Lcs251/lab2/GomokuModel;)V from class Gomoku
at Gomoku.main(Gomoku.java:47)
This particular error is giving me trouble. I've never seen anything like it, and my research on the web doesn't turn up anything. Because the error says it's coming from GomokuGUI, which is one of the lab2.jar files, I think the error's on my end. My questions are:
Can I make an executable .jar when I know and have
What goes in the classpath
Where the main should be
A set of relevant class files
If the answer to (1) is yes: Am I going about it in the right way? I have a feeling I'm missing a recompile step somewhere.
In this particular case, I may ask the student to resubmit. And I will download the .jar's I see submitted before due date to make sure they are runnable. But for knowledge's sake (I myself have made .jar files that have had only .class in them and no manifest), is there a way to salvage a working file like the one described above?
From the JRE javadoc:
public class IllegalAccessError
extends IncompatibleClassChangeError
Thrown if an application attempts to access or modify a field, or to
call a method that it does not have access to.
You're getting
0Exception in thread "main" java.lang.IllegalAccessError: tried to access method
cs251.lab2.GomokuGUI.<init>(Lcs251/lab2/GomokuModel;)V from class Gomoku
at Gomoku.main(Gomoku.java:47)
The method it's complaining about is named <init>. That's what Java calls constructors, internally. It's saying that Gomoku.main() tried to issue new GomokuGUI(model) where model is expected to be an instance of GomokuModel, but that this constructor was not accessible. The fact that Gomoku.main() is in a different package from GomokuGUI means the constructor would have to be public for that to work.
You can check that via reflection -- I believe Eclipse can do that for you, actually -- but that's almost certainly what's going on.
So either the student turned in broken code, or you broke it during your attempts to force-fit it into convenience-executable jarfile format. Which was wasted effort in any case, since you can't grade the assignment based on object code and you're going to have to go back and ask for source code anyway.
If you really want to try running the jarfile the student submitted: Go back to the original unmodified jarfile and try just running 'java Gomoku -classpath myJar.jar' where myJar.jar is what the student turned in. If that doesn't work, try 'java Lcs251.lab2.Gomoku -classpath myJar.jar', which is probably the package they intended to put it into given the error message you're getting. If neither of those runs, ask the student what command line they've been using to run it and try that. If THAT doesn't work, then it's time to investigate why.
The whole executable-jar question is a red herring and a waste of time until you know the code actually runs and what the entry point actually is.
I'm trying to create a simple .jar file out of my project. The project is made of two .class files - the main class which uses the secondary class to generate a GUI. The main class is the actual "main" class that runs while the second class is just a class file with it's methods and it's also an extension of JFrame and imports javax.swing and java.awt.event.*.
I use Jar to bundle it all up. I add a manifest file (with a new line character) which points to the primary file with the main method. The Jar file thus has two .class files and a folder with the manifest.txt in it. When I use javaw.exe to run it, nothing happens at all. So I try to run it in the command line and I get a NoClassDefFroundError about the secondary class.
I noticed I get the same kind of error when I try to compile and run the second class in JCreator - no wonder, it doesn't have a main method, it's just a class file. When I run the main file from JCreator, everything works fine.
Any ideas?
Looking at your stack trace, I can now see the problem: I can tell you actually have more than two classes:
Caused by: java.lang.ClassNotFoundException: grafPrime$calcButton at
There's a file named grafPrime$calcButton.class, and it needs to be in the jar file, too. There may be other such files -- make sure you include all of them!
Okay, the problem is that you've not included the anonymous class - you should have a file called grafPrime$calcButton.class, and that's not in your jar file.
Basically, compile your code into a clean directory and include all the class files which are generated.