Question

I create jar file with command.

$jar -cvf A.jar A.class

I tried executing

$java -jar A.jar 

I am getting below error.(Before adding “Main-class : A” to manifest.mf)

Failed to load Main-Class manifest attribute from A.jar

contents of MANIFEST.MF

Manifest-Version: 1.0

Created-By: 1.6.0_18 (Sun Microsystems Inc.)
Main-Class: A

Now i am getting

Exception in thread "main" java.lang.NoSuchMethodError: main

Answer 1

Usually you don’t need to specify an Manifest file when you create a jar, but as you want to start your jar by launching java -jar you must specify your own manifest which details where is the class containing the main() method.

In order to do this you have to create a file containing this line :

Main-Class: A

(I suppose A is your class containing your main method, if it isn’t the case specify the FQN of your desired class)

and create your jar with the following command :

jar cfm A.jar yourFileContainingMain-Class A.class

For example :

//Mac-Makkhdyn:~ Makkhdyn$ cat A.java
public class A{
public static void main(String... args){
System.out.println("lol");
}
}
//Mac-Makkhdyn:~ Makkhdyn$ cat manifest 
Main-Class: A
//Mac-Makkhdyn:~ Makkhdyn$ javac A.java
//Mac-Makkhdyn:~ Makkhdyn$ jar cvfm A.jar manifest A.class 
added manifest
adding: A.class(in = 399) (out= 278)(deflated 30%)
//Mac-Makkhdyn:~ Makkhdyn$ java -jar A.jar
lol

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After your edit :

You must have a main() method in your A class you want to launch. Check the link below.

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Resources :

• oracle.com – Setting an Application’s Entry Point