[1.8.9] How to check if a player name is connected to the server?

[WaningMatrix]

I want to check if a player is connected to the server or not like if say Player A joins a server and there is another Player B in the game [like in TAB list] and if the player is there do something and if not do nothing. How do I do it?

 

Secondary Query:

Also if I have a Array list defined in the program and I keep giving it values and restart minecraft, does the ArrayList gets cleared or not? If yes let me know how can I get a ArrayList to be stored permanently which the user can still edit anytime in game simply by using a command. Or give me a forum link or something.

 

Please let me know how do I do this and answer my secondary query as well if you got a answer to it as well.

 

[Cadiboo]

1.8.9 is no longer supported on these forums due to its age (no-one knows how to make mods for it anymore) are you willing to update to 1.12.2 (if you aren't you won't receive support)