How do I automate selecting files in a .jar file?

My .jar file has a number of buttons that, when clicked, prompts me to select a file to load. I need to find a way to get this file selection to be automated, and decided on applescript.

Unfortunately, so far I have not been able to get keystroke to work when the "select file" screen comes up.

So far, I have:

  tell application "System Events" to set frontmost of process "java" to true
  tell application "System Events"
      tell process "java"
          keystroke tab & tab & tab & tab & tab & tab
          key code 76 using {keystroke space}
      end tell
  end tell

because using this does not work:

  tell application "System Events" to set frontmost of process "java" to true
  tell application "System Events"
      tell process "java"
          keystroke tab & tab & tab & tab & tab & tab
          key code 76 using {keystroke space} --- stops here
          key code 124
          key code 76
      end tell
  end tell