Error: Could Not Find Main Class. Program Will Exit

A Friend Of Mine Made A .jar File
But Hes Not in Contact With Me Since Long Time. I Edit His .jar File Using Winzip unzippin it n again packing it ....
But After Editing That File i Cant Run It.

this error comes

Could Not Find Main Class. Program Will Exit

have he done some type of security ? that no1 can edit it ?
im so confused because even if i dont change anything in those .class file just save it .. the .jar Gives That error
Thanks

i presume when u said u run da jar file meaning u double click da jar file n it gives da "Could Not Find Main Class" message?

have u made the manifest file (.mf) and packed it together inside da jar with the rest of ur .class files?

Da manifest file are used to tell the computer what .class should be used when u click da .jar file, .jar dun really work like .exe files, maybe thats da problem :p

This will surely help.....

I recommend you download Blue J. its free and will let you JAR your file from within its interface without the need of command prompt. you just load up your classes into blue j and select "create JAR" or something similar (not using blue j right now) and you choose which main method (if you have more than one) you would like to execute primarily.