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.

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: /a/63815140/7438905

You can use mvn dependency:tree to visualize the dependency tree.

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

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 following scenario:

..SomePath>javac HelloWorld.java
..SomePath>java HelloWorld.class

In other words, use:

..SomePath>java HelloWorld

P.S. The addition to 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 Variable’s PATH.
P.P.S. Was I correct in my assumption/s?

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

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.

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.

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

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.

1. It could happen if your classpath is not correct

2. 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.

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.

1. Right Click on class > Run as > Run Configuration
2. remove main class reference
3. Apply > Close
4. 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:codeprototype-apptargetclasses>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.

On my case, I´m using Spring Tool Suite 4, and my problem was solved doing that two steps:

1. Right Click on the project –> Run As –> Maven clean.
2. Right Click on the project –> Run As –> Maven install.

Then I could run the project with:
Run As –> Spring Boot App.

Hope It helps someone 🙂

Passing the package name is the key and classname along with the jar file, After running the mvn package command.

Run the following by modifying the Jar and package name as per below.

java -cp targetTest-1.0-SNAPSHOT.jar com.compname.Test

When I tried to link library I got error as below

root@thpritam:/home/thpritam/classes# java -cp /home/thpritam/classes/spring-boot-3.3.4.jar org.springframework.boot.SpringApplication

Error: LinkageError occurred while loading main class org.springframework.boot.SpringApplication
java.lang.UnsupportedClassVersionError: org/springframework/boot/SpringApplication has been compiled by a more recent version of the Java Runtime (class file version 61.0), this version of the Java Runtime only recognizes class file versions up to 55.0

This means it’s a java version error and I have to upgrade my java or include old version library.

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.