New to Java

I have created a .jar file in eclipse, which when imported back into a new project it runs, only once.

Then it says the jar has no main method. Have to restart eclipse and actually go to the class with the main to run it.

If I run the jar through the terminal I get an error "invalid or corrupt jarfile"

Double clicking the jar file doesn't work either.

I have no idea what the error is.

any help appreciated.

Regards