Currently to launch executable jar it is required to use following syntax
    java -jar a.jar

The request here is to allow for
     java a.jar

This is important for scenario where jar is launched by doubleclick.
Windows and window managers on Linux allow user to select what program should be used for files with specific extension.
However, they do not provide UI to specify command format. Hence there is no easy way for user to
create association manually. JRE installers create default associations but this does not work for all users
(may have user association created for various reasons and then it is not easy to fix).

Technically, this request means java launcher should distinguish whether it is request to launch class or jar file
but this should be fairly easy to detect by checking magic numbers in the file.