Could not find or load main class

Could not find or load main class - java

I have Windows 7, installed jdk1.7.0 and its supporting jre7.
My problem is compilation part works perfectly, but while running the Java program I get this error saying:
"Could not find or load main class"
I am storing all my programs in javalab folder. I have set the path to it. Procedure looks like this:
C:\Users\user>cd\
C:\>cd javalab
C:\javalab>autoexec.bat
C:\javalab>set path=C:\Program Files\Java\jdk1.7.0\bin
C:\javalab>javac p1.java
C:\javalab>java p1
Error: Could not find or load main class p1
C:\javalab>

I was having a similar issue with my very first java program.
I was issuing this command
java HelloWorld.class
Which resulted in the same error.
Turns out you need to exclude the .class
java HelloWorld

Try:
java -cp . p1
This worked for me when I had the same problem, using Fedora (linux)

Simple way to compile and execute java file.(HelloWorld.java doesn't includes any package)
set path="C:\Program Files (x86)\Java\jdk1.7.0_45\bin"
javac "HelloWorld.java"
java -cp . HelloWorld
pause

javac should know where to search for classes. Try this:
javac -cp . p1.java
You shouldn't need to specify classpath. Are you sure the file p1.java exists?

I had almost the same problem, but with the following variation:
I've imported a ready-to-use maven project into Eclipse IDE from PC1 (project was working there perfectly) to another PC2
when was trying to run the project on PC 2 got the same error "Could not find or load main class"
I've checked PATH variable (it had many values in my case) and added JAVA_HOME variable (in my case it was JAVA_HOME = C:\Program Files\Java\jdk1.7.0_03)
After restarting Ecplise it still didn't work
I've tried to run simple HelloWorld.java on PC2 (in another project) - it worked
So I've added HelloWorld class to the imported recently project, executed it there and - huh - my main class in that project started to run normally also.
That's quite odd behavour, I cannot completely understand it.
Hope It'll help somebody. too.

i guess that you have a different class name in p1.java

Check you class name first. It should be p1 as per your batch file instruction. And then check you package of that class, if it is inside any package, specify when you run.
If package is x.y
java x.y.p1

Here is my working env path variables after much troubleshooting
CLASSPATH
.;C:\Program Files (x86)\Java\jre7\lib\ext\QTJava.zip;C:\Program Files (x86)\Java\jdk1.6.0_27\bin
PATH <---sometimes this PATH fills up with too many paths and you can't add a path(which was my case!)
bunchofpaths;C:\Program Files (x86)\Java\jdk1.6.0_27\bin
Additionally, when you try to use the cmd to execute the file...make sure your in the local directory as the file your trying to execute (which you did.)
Just a little checklist for people that have this problem still.

I've had similar problems. If you work with Eclipse, you need to go to the folder where you have your src/ folder... If you used a package - then you use
javac -cp . packageName/className
which means if you've had a package named def and main class with name TextFrame.java you'd write
javac -cp . def/TextFrame
omitting the trailing .java extension, and then you run it with the
java def/TextFrame
and if you have have arguments, then you need to supply it with arguments corresponding to your program.
I hope this helps a bit.

First, put your file *.class (e.g Hello.class) into 1 folder (e.g C:\java). Then you try command and type cd /d C:\java. Now you can type "java Hello" !

You might have the CLASSPATH environment variable already added!!
Use following to avoid further usage of -cp . in java -cp . CLASSFILE
Add . to CLASSPATH in system properties->environment variables or by cmd
set CLASSPATH=%CLASSPATH%;.;

I faced a similar problem in Eclipse. Whenever I clicked on the Run button it gave me the message, "Error: Could not find or load main class". But when I right click on the java file in the project explorer and Run As Java configuration, it works perfectly.
I think this is because it tries by default to run it in some other configuration which causes problems.
Hope this answer helps some.

If you have a single .java file to compile using command-line , then remove
topmost package parts from the code, the compile again, it will work.
This worked for me.

Sometimes what might be causing the issue has nothing to do with the main class. I had to find this out the hard way, it was a referenced library that I moved and it gave me the:
Could not find or load main class xxx Linux
I just delete that reference and added again and it worked fine again.

i had
':'
in my project name e.g 'HKUSTx:part-2'
renaming it 'HKUSTx-part-2' worked for me

You can use NetBeans IDE which is free to download and use "Open Source". You can even do other programming language in this IDE. The latest of which it supports HTML5. This makes your programming easier. If you're not familiar with it choose a book that is NetBeans integrated like Sams Teach Yourself Java in 24 Hours

Related

Error: Could not find or load main class fileReader.Main Caused by: java.lang.ClassNotFoundException: fileReader.Main (individual case) [duplicate]

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();
}

Package does not exist error when package was added to classpath

Note, linked solutions (ex. Fatal Error: Unable to find package java.lang in classpath or bootclasspath) do not work.
I get this error, but the package is imported (commons... .jar)
org.apache.commons.lang3.tuple //does not exist import
org.apache.commons.lang3.tuple.MutableTriple
Source code
import org.apache.commons.lang3.tuple.MutableTriple;
import org.apache.commons.lang3.tuple.Pair;
import org.apache.commons.lang3.tuple.Triple;
Build code:
export
JAVA_HOME=/Library/Java/JavaVirtualMachines/jdk1.8.0_25.jdk/Contents/Home
/Library/Java/JavaVirtualMachines/jdk1.8.0_25.jdk/Contents/Home/bin/javac
-target 1.8 -source 1.8 -classpath \ "../lib/commons-lang3-3.4.jar;../lib/httpclient-4.5.jar;../lib/httpcore-4.4.1.jar;../lib/org.json-20120521.jar;../lib/pdfbox-app-2.0.0-20150606.170503-1383.jar;../src/:../lib/commons-lang3-3.4-javadoc.jar;../lib/pdfbox-app-2.0.0-20150606.170503-1383-sources.jar" \ -d output \ ../src/com/tymaf/pdf/*.java
How to fix this problem?

Double check your classpath. Looks like you mixed delimiters ; and :.
Also instead of including jar with compiled classes (library itself). You've included java-docs and sources that are useless in classpath.
../src/:
../lib/commons-lang3-3.4-javadoc.jar;
../lib/pdfbox-app-2.0.0-20150606.170503-1383-sources.jar

Here is my suggestion
How to compile and use .jar extension
.jar extension can be imported different ways depending on your environment and IDE.
Here how it work as native mode from console.
Download the .jar.zip library from
http://www.java2s.com/Code/Jar/c/Downloadcommonslang333jar.htm
Create a folder in your working (project) directory call it libs
Unzip the downloaded file and copy commons-lang3-3.3.jar to your working directory libs
I have also created a class just for testing call it TheNewWork.java and added the 3 imports.
Now from your working directory c:\projects for Compile:
javac -classpath "/Projects/libs/commons-lang3-3.3.jar;" TheNewWork.java
And for running it:
java -classpath "/Projects/libs/commons-lang3-3.3.jar;" TheNewWork
If you have more than one .jar just add ; for Windows and : for Linux. Btw I use windows 10 cmder console and java jdk1.8.0_66. In other OS console you might need to put .:Projects...etc in stead of /Projects...etc. but the idea is the same.
UPDATE
In windows it is possible to set classpath like
set CLASSPATH=%CLASSPATH%;C:\Projects\libs\commons-lang3-3.3.jar
OR in Linux
export CLASSPATH=".:/Projects/libs/commons-lang3-3.3.jar"
Then you can run javac TheNewWork.java but it is personal taste to do it this or the other way. Some things similar is also possible to do in other OS.
Last thing, if you lazy and do neither want to write a full command line nor create a classpath, you could create a batch file with the full command line and run it that way in stead ;)
Some references:
http://docs.oracle.com/javase/8/docs/technotes/tools/windows/classpath.html
https://www3.ntu.edu.sg/home/ehchua/programming/howto/JDK_Howto.html
https://www.chilkatsoft.com/java-classpath-Windows.asp
I hope this solves your problem
Before the solution
After the solution
NOTE
In addition thanks to #MarkPeters notified me on my previous answer: Adding application dependencies directly to the JRE libs is not a good approach, as it makes the JRE suitable for running only one Java application, rather than being a generic runtime. Plus it would complicate whatever deployment the OP wants to do. lib/ext is made for extending the core Java APIs, as described here: docs.oracle.com/javase/tutorial/ext/basics/install.html. Not for normal application dependencies.