I know you can compile java programs into a single .jar file that you can execute but I have a problem and I want to know if it can be solved. Now I have a custom file format that has the extension .dta the files contain some data to create a graph. Now I want to be able to double click these files and have them open in my java program. Also if the program is already open I want any further files that are opened (not via the file > open functionality) to open in this same instance of the application. How can I do this and what would be the best way. Should I use a separate launcher application written in say C# that calls the java -jar application.jar filename? Or is there an easier way to do this. Thanks in advance.