MacOS launcher should let the user know if Java is not available

[jackjansen]

I was going to write a bug report "doesn't work on MacOS 11", but it turns out the problem was that Java is no longer installed by default.

There is indeed a small notice on the download page that you should "install java 8", but I overlooked that.

It would be sort of nice if the app would pop up a dialog if Java is missing on your machine, few people will have it installed nowadays... And right now the app does absolutely nothing if you double-click it without Java installed.

[angryziber]

Do you know how to popup a GUI dialog on macOS from command-line?

[llamafilm]

@angryziber there are several ways but one easy option is Apple Script: osascript -e 'display dialog "You must install Java first" with icon stop with title "Angry IP Scanner"'

[angryziber]

It's interesting that if you type java in the terminal, macOS would open a dialog prompting to install Java. Doesn't it happen if you try to run ipscan for the first time?