I cant run any jar files

[Davy Kelly]

Hey everyone,

I cannot run any jar files.

I downloaded Derby today to play around with databases

I get this error all the time:
"Failed to load Main-Class manifest attribute from
C:\Derby_10\lib\derby.jar"

why is this?

Oh and any other Jars I download is the exact same

davy

[Jeff Mayer]

Davy,

Not every jar file is runnable.
Let's suppose that you create a set of utility classes that you would like to assemble and distribute as a jar file.

It is very probable that none of the classes contained in your jar file has a main method. Maybe it wouldn't even make any sense to have any main method in your classes.

Just to begin with, you cannot directly "run" a jar file if there is no main method to be called in any of its classes. Even if a main method exists, if you would like to run it this way:

java -jar myjarfile.jar

you would need to include a Main-Class entry in the jar's manifest file.

In the case of Derby, you should read its documentation, which explains how you are supposed to use it.