Error during conversion of .class file to jar file

I am unable to understand the reason behind the error.I want to convert .class file to jar file,

on dos i write :

java cf myjar.jar *.class

but here is what i get in return:

Error: Could not find main class cf Exception in thread "mai开发者_JS百科n" java.lang.NoClassDefFoundError: cf

---and goes on,,,,

Why i am getting this error and what is it?

You're running the wrong command - java instead of jar. That's why it's treating cf as a class name.

You want:

jar cf myjar.jar *.class

First you need to use the jar command, java command is to running while the jar command will create the .jar file.

You also need to include a manifest file, which will determine the main class of your application. See Working with Manifest Files. Without a manifest file you will need to specify the main class when running the app, like "java -cp JARFILE.jar package.MyMain"