Develop Reference

Cannot run a .jar file

I'm having issues when I try to execute a .jar file. I always get the message from the command prompt "cannot find or load main class" every time I try to run the file I have just compiled.
I have tried the following(using the command prompt and saving the java code with Notepad++ and creating the manifest.txt file in the same folder where the .java code was saved):
javac classname.java
java cfm classname.jar manifest.txt classname.class
java -jar classname
I have also tried:
javac classname.java
java classname
And:
java packagename.classname
After compiling the .java file
I know there are hundreds of questions like this in the forums, but I have looked everywhere and I keep getting the same error. I just cannot run the .jar file even after I create it.
It's probably something I have missed but I am out of ideas.
Manifest:
Main-Class: classname

Let's see.
java -jar classname.jar
would work if your MANIFEST.MF calls out the correct class.
java -cp classname.jar my.package.MyClass
would work in any case.

.jar error - could not find or load main class

I tried to put HelloWorld in a .jar file and running it, but it doesn't work. I created the java file and typed in the program, and then wrote in cmd:
javac HelloWorld.java
java HelloWorld
and it worked. Then I entered
echo Main-Class: HelloWorld >manifest.txt
jar cvfm HelloWorld.jar manifest.txt HelloWorld.class
and got the output
added manifest
adding: HelloWorld.class(in = 426) (out= 288)(deflated 32%)
I then entered
java -jar HelloWorld.jar
HelloWorld.jar
and the first line worked, while the second line gave me an error:
Error: Could not find or load main class path\HelloWorld.jar
which is the same output I got (in a rapidly closing window) when I tried to open it with the java.exe file in 64 bit jre7\bin, jdk1.7.0_51\bin, jdk1.7.0_51\jre\bin, as well as 32 bit jre7\bin. I've uninstalled and reinstalled both my jre and jdk and recreated my .class and .jar files, but the problem persists. I'm on win8.
Edit: I tried to do as aetheria suggested, but no luck. I put HelloWorld.java in path\com\stackoverflow\user\blrp, compiled it, and it worked by entering
java com.stackoverflow.user.blrp.HelloWorld
in path. I then created the manifest and jar by:
(echo Manifest-Version: 1.0
echo Class-Path: .
echo Main-Class: com.stackoverflow.user.blrp.HelloWorld) >manifest.txt
jar cvfm HelloWorld.jar manifest.txt com\stackoverflow\user\blrp\HelloWorld.class
and got the output
added manifest
adding: com/stackoverflow/user/blrp/HelloWorld.class(in = 454) (out= 312)(deflat
ed 31%)
but still, java -jar HelloWorld.jar worked and HelloWorld.jar didn't (same error). I also tried not doing the package thing, just the Class-Path in manifest, same result.
(Also, I solved the problem prior to asking the question by use of a .bat file, but it'd still be sweet to get that jar working.)

Thanks jbaliuka for the suggestion. I opened the registry editor (by typing regedit in cmd) and going to HKEY_CLASSES_ROOT > jarfile > shell > open > command, then opening (Default) and changing the value from
"C:\Program Files\Java\jre7\bin\javaw.exe" -jar "%1" %*
to
"C:\Program Files\Java\jre7\bin\java.exe" -jar "%1" %*
(I just removed the w in javaw.exe.) After that you have to right click a jar -> open with -> choose default program -> navigate to your java folder and open \jre7\bin\java.exe (or any other java.exe file in you java folder). If it doesn't work, try switching to javaw.exe, open a jar file with it, then switch back.
I don't know anything about editing the registry except that it's dangerous, so you might wanna back it up before doing this (in the top bar, File>Export).

I found this question when I was looking for the answer to the above question. But in my case the issue was the use of an 'en dash' rather than a 'dash'. Check which dash you are using, it might be the wrong one. I hope this answer speeds up someone else's search, a comment like this could have saved me a bit of time.

You can always run this:
java -cp HelloWorld.jar HelloWorld
-cp HelloWorld.jar adds the jar to the classpath, then HelloWorld runs the class you wrote.
To create a runnable jar with a main class with no package, add Class-Path: . to the manifest:
Manifest-Version: 1.0
Class-Path: .
Main-Class: HelloWorld
I would advise using a package to give your class its own namespace. E.g.
package com.stackoverflow.user.blrp;
public class HelloWorld {
...
}

Had this problem couldn't find the answer so i went looking on other threads, I found that i was making my app with 1.8 but for some reason my jre was out dated even though i remember updating it. I downloaded the lastes jre 8 and the jar file runs perfectly. Hope this helps.

How to run Java program in command prompt

I created a Java project to call a Web service.
It has one Main java file and another class file.
I have used some jar files for HTTP client.
In Eclipse it runs fine.
I need to run the Java program in command prompt by passing some arguments.
In command prompt I went to src folder containing main java and sub class java file and gave the following command
javac mainjava.java
I'm getting following error
mainjava.java:14: cannot find symbol
symbol : class SubClass
here SubClass is my another java class file used to call the web service.
How to run the program by passing arguments?

javac is the Java compiler. java is the JVM and what you use to execute a Java program. You do not execute .java files, they are just source files.
Presumably there is .jar somewhere (or a directory containing .class files) that is the product of building it in Eclipse:
java/src/com/mypackage/Main.java
java/classes/com/mypackage/Main.class
java/lib/mypackage.jar
From directory java execute:
java -cp lib/mypackage.jar Main arg1 arg2

A very general command prompt how to for java is
javac mainjava.java
java mainjava
You'll very often see people doing
javac *.java
java mainjava
As for the subclass problem that's probably occurring because a path is missing from your class path, the -c flag I believe is used to set that.

You can use javac *.java command to compile all you java sources. Also you should learn a little about classpath because it seems that you should set appropriate classpath for succesful compilation (because your IDE use some libraries for building WebService clients). Also I can recommend you to check wich command your IDE use to build your project.

All you need to do is:
Build the mainjava class using the class path if any (optional)
javac *.java [ -cp "wb.jar;"]
Create Manifest.txt file with content is:
Main-Class: mainjava
Package the jar file for mainjava class
jar cfm mainjava.jar Manifest.txt *.class
Then you can run this .jar file from cmd with class path (optional) and put arguments for it.
java [-cp "wb.jar;"] mainjava arg0 arg1
HTH.

javac only compiles the code. You need to use java command to run the code. The error is because your classpath doesn't contain the class Subclass iwhen you tried to compile it. you need to add them with the -cp variable in javac command
java -cp classpath-entries mainjava arg1 arg2 should run your code with 2 arguments

Problems compiling and running Java app with Bluecove (NoClassDefFoundError)

I have this app that uses bluetooth, so I need both, bluecove and bluecove-gpl packages, when I run it in NetBeans I have no problem at all, and works perfectly fine. But I still can't compile and run from the command line (Ubuntu 11.04).
I'm using this line for compilation:
$ javac -Xlint:unchecked -classpath bluecove-2.1.0.jar:bluecove-gpl-2.1.0.jar Client.java
And it doesn't return errors and it generates a .class file
Then I try to run the .class file like this:
java -classpath bluecove-2.1.0.jar:bluecove-gpl-2.1.0.jar Client
But it returns a NoClassDefFoundError.
Could not find the main class: SPPClient.
Why is this happening?

You probably need to add your current directory (or whatever directory your class files reside in) to the class path.
Try something like
java -classpath .:bluecove-2.1.0.jar:bluecove-gpl-2.1.0.jar Client
or
java -classpath bin:bluecove-2.1.0.jar:bluecove-gpl-2.1.0.jar Client

You need to have the main class definition in the manifest file:
Main-Class: classname

How to run a JAR file

I created a JAR file like this:
jar cf Predit.jar *.*
I ran this JAR file by double clicking on it (it didn't work). So I ran it from the DOS prompt like this:
java -jar Predit.jar
It raised "Failed to load main class" exceptions. So I extracted this JAR file:
jar -xf Predit.jar
and I ran the class file:
java Predit
It worked well. I do not know why the JAR file did not work. Please tell me the steps to run the JAR file

You need to specify a Main-Class in the jar file manifest.
Oracle's tutorial contains a complete demonstration, but here's another one from scratch. You need two files:
Test.java:
public class Test
{
public static void main(String[] args)
{
System.out.println("Hello world");
}
}
manifest.mf:
Manifest-version: 1.0
Main-Class: Test
Note that the text file must end with a new line or carriage return.
The last line will not be parsed properly if it does not end with a
new line or carriage return.
Then run:
javac Test.java
jar cfm test.jar manifest.mf Test.class
java -jar test.jar
Output:
Hello world

java -classpath Predit.jar your.package.name.MainClass

Before run the jar check Main-Class: classname is available or not in MANIFEST.MF file. MANIFEST.MF is present in jar.
java -jar filename.jar

You have to add a manifest to the jar, which tells the java runtime what the main class is.
Create a file 'Manifest.mf' with the following content:
Manifest-Version: 1.0
Main-Class: your.programs.MainClass
Change 'your.programs.MainClass' to your actual main class. Now put the file into the Jar-file, in a subfolder named 'META-INF'. You can use any ZIP-utility for that.

A very simple approach to create .class, .jar file.
Executing the jar file. No need to worry too much about manifest file. Make it simple and elgant.
Java sample Hello World Program
public class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello World");
}
}
Compiling the class file
javac HelloWorld.java
Creating the jar file
jar cvfe HelloWorld.jar HelloWorld HelloWorld.class
or
jar cvfe HelloWorld.jar HelloWorld *.class
Running the jar file
java -jar HelloWorld.jar
Or
java -cp HelloWorld.jar HelloWorld

If you don`t want to create a manifest just to run the jar file, you can reference the main-class directly from the command line when you run the jar file.
java -jar Predit.jar -classpath your.package.name.Test
This sets the which main-class to run in the jar file.

Java
class Hello{
public static void main(String [] args){
System.out.println("Hello Shahid");
}
}
manifest.mf
Manifest-version: 1.0
Main-Class: Hello
On command Line:
$ jar cfm HelloMss.jar manifest.mf Hello.class
$ java -jar HelloMss.jar
Output:
Hello Shahid

Eclipse Runnable JAR File
Create a Java Project – RunnableJAR
If any jar files are used then add them to project build path.
Select the class having main() while creating Runnable Jar file.
Main Class
public class RunnableMainClass {
public static void main(String[] args) throws InterruptedException {
System.out.println("Name : "+args[0]);
System.out.println(" ID : "+args[1]);
}
}
Run Jar file using java program (cmd) by supplying arguments and get the output and display in eclipse console.
public class RunJar {
static StringBuilder sb = new StringBuilder();
public static void main(String[] args) throws IOException {
String jarfile = "D:\\JarLocation\\myRunnable.jar";
String name = "Yash";
String id = "777";
try { // jarname arguments has to be saperated by spaces
Process process = Runtime.getRuntime().exec("cmd.exe start /C java -jar "+jarfile+" "+name+" "+id);
//.exec("cmd.exe /C start dir java -jar "+jarfile+" "+name+" "+id+" dir");
BufferedReader br = new BufferedReader(new InputStreamReader(process.getInputStream ()));
String line = null;
while ((line = br.readLine()) != null){
sb.append(line).append("\n");
}
System.out.println("Console OUTPUT : \n"+sb.toString());
process.destroy();
}catch (Exception e){
System.err.println(e.getMessage());
}
}
}
In Eclipse to find Short cuts:
Help ► Help Contents ► Java development user guide ► References ► Menus and Actions

I have this folder structure:
D:\JavaProjects\OlivePressApp\com\lynda\olivepress\Main.class
D:\JavaProjects\OlivePressApp\com\lynda\olivepress\press\OlivePress.class
D:\JavaProjects\OlivePressApp\com\lynda\olivepress\olives\Kalamata.class
D:\JavaProjects\OlivePressApp\com\lynda\olivepress\olives\Ligurian.class
D:\JavaProjects\OlivePressApp\com\lynda\olivepress\olives\Olive.class
Main.class is in package com.lynda.olivepress
There are two other packages:
com.lynda.olivepress.press
com.lynda.olivepress.olive
1) Create a file named "Manifest.txt" with Two Lines, First with Main-Class and a Second Empty Line.
Main-Class: com.lynda.olivepress.Main
D:\JavaProjects\OlivePressApp\ Manifest.txt
2) Create JAR with Manifest and Main-Class Entry Point
D:\JavaProjects\OlivePressApp>jar cfm OlivePressApp.jar Manifest.txt com/lynda/olivepress/Main.class com/lynda/olivepress/*
3) Run JAR
java -jar OlivePressApp.jar
Note: com/lynda/olivepress/* means including the other two packages mentioned above, before point 1)

If you don't want to deal with those details, you can also use the export jar assistants from Eclipse or NetBeans.

Follow this answer, if you've got a jar file, and you need to run it
See troubleshooting sections for hints to solve most common errors
Introduction
There are several ways to run java application:
java -jar myjar.jar - is the default option to run application
java -cp my-class-path my-main-class or java -classpath my-class-path my-main-class
java --module-path my-module-path --module my-module/my-main-class
Deployment to an enterprise server. It's when you have war or ear file. We'll omit the explanation for this
case
In this answer I'll explain, how to run a jar if you have to run it manually, give hints to resolve common problems.
java -jar
Start with the most common option: run the jar file using the -jar. Example:
java -jar myjar.jar
If it fails:
with no main manifest attribute, then the jar is not executable:
If you're trying to build a jar
see Can't execute jar- file: "no main manifest attribute"
Otherwise, proceed with classpath or module-path solution below
with other error, then see "Troubleshooting" section below
Classpath or module path
If -jar failed, then the jar should be run using classpath or module-path.
Module-path is used, when an application is modular itself.
JPMS - Java Platform Module System - is a modern way to develop, distribute and run applications. For details:
Watch excellent Modular Development with JDK 9 by Alex Buckley
See awesome-java-module-system
To run a jar:
Determine if it's modular or not:
Invoke:
jar --describe-module --file=path-to-jar-file
Examine output:
If you see No module descriptor found. in the first line, then proceed with classpath solution below
If you see something similar to:
org.diligentsnail.consoleconsumer#1.0-SNAPSHOT jar:file:///home/caco3/IdeaProjects/maven-multi-module-project-demo/jars/console-consumer.jar!/module-info.class
requires java.base mandated
requires org.diligensnail.hellolibrary
continue with module-path solution below
See also: List modules in jar file
Classpath
Try the following:
java -cp my-jar.jar my-main-class
-cp is the same as -classpath
my-jar.jar is the jar to run
my-main-class is name of the class with static void main(String[]) method
Example:
java -cp jars/console-consumer.jar org.diligentsnail.consoleconsumer.Main
Module-path
Try the following command:
java --module-path my-jar.jar --module my-module-name/my-main-class
my-jar.jar is the jar to run
my-module-name is name of the module where my-main-class belongs
Usually my-module-name is in the module-info.java file
my-main-class - the class with the static void main(String[]) method
If it fails with FindException:
Example of message:
Error occurred during initialization of boot layer
java.lang.module.FindException: Module javafx.fxml not found, required by org.diligentsnail.javafxconsumer
Usually, this means the my-jar.jar has a dependency on the other jar.
For example, the application uses a third party library.
See "Supplying dependencies" below
Troubleshooting
UnsupportedClassVersionError
Update java. See List of Java class file format major version numbers?
NoClassDefFoundError, NoSuchMethodError, NoSuchFieldError
See:
"Supplying dependencies" section
Why am I getting a NoClassDefFoundError in Java?
Supplying dependencies
An Error or Exception is thrown when an application run with missing or out of date dependencies.
Common exceptions and errors:
NoClassDefFoundError, NoSuchFieldError, NoSuchMethodError
ClassNotFoundException, NoSuchFieldException, NoSuchMethodException
FindException
To supply dependencies:
Determine the list of dependencies
Usually it's a list of jar or can be a list of directories or both
Join the list with : if you're running Unix, ; - if you're on Windows
Invoke java with -classpath or --module-path
Example
Project maven-multimodule-project-demo
I'm trying to run console-consumer.jar:
Command:
java -classpath jars/console-consumer.jar org.diligentsnail.consoleconsumer.Main
jars/console-consumer.jar is the jar I'm trying to run
org.diligentsnail.consoleconsumer.Main is the class with main method
Error I get:
Exception in thread "main" java.lang.NoClassDefFoundError: org/diligentsnail/hellolibrary/Hello
at org.diligentsnail.consoleconsumer.Main.main(Main.java:11)
Caused by: java.lang.ClassNotFoundException: org.diligentsnail.hellolibrary.Hello
at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:641)
at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:188)
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:520)
... 1 more
Missing dependency is jars/hello-library.jar
Correct command:
java -classpath jars/console-consumer.jar:jars/hello-library.jar org.diligentsnail.consoleconsumer.Main

To run jar, first u have to create
executable jar
then
java -jar xyz.jar
command will work