How to tell what program will open a particular file extension

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Command	Step-by-Step	Explanation
Open a command prompt	From the Start Menu, choose Run... Type CMD Press OK	These are command-line programs that must be run from a command prompt.
Run the ASSOC command	Type assoc .ext (where .ext is the extension you are interested in) You should see something like .ext=MyExtFile. You will use theMyExtFile value in the next step.	This displays the "Association" for this extension. There isn't much you can do with this except the next step.
Run the FTYPE command	Type ftype MyExtFile (where MyExtFile is the value obtained in the previous step)	This shows the command line that will be used to open files with this association.

Open a command prompt window using "Run as administrator”, and then type: -

C:\>assoc .jar=jarfile

C:\>ftype jarfile="C:\Program Files (x86)\Java\jre7\bin\javaw.exe" -jar "%1" %*