The jar file is actually the application. Jad files are just descriptive and give some info on how the jar is to run.
If you open up the jad file with wordpad you will see a line that looks like this.
MIDlet-Jar-URL: http://mini.opera.com/dl/UP*uWyaNvV4FTOWByTwAQFCADw8CZGVmYXVsdC5wbmc=/mini.jarSo if you upload the jad to davidpye or waphq it will know where to find the jar file.
But if it looks like this
MIDlet-Jar-URL: opera mini.jarThen you will have to find the jar file on your own.
But if you are installing using TKFE you will have to find the jar file yourself. Sometimes like the first opera mini url you can copy and paste that in the browser on your pc and it will download to your pc.