Try doing this:
Player targetPlayer = Bukkit.getServer().getPlayer(args[0]);
//or this:
Player targetPlayer = plugin.getServer().getPlayer(args[0]);
instead of
Player targetPlayer = player.getServer().getPlayer(args[0]);
and the same thing here, replace:
if(player.getServer().getPlayer(args[0]) !=null){
with:
if(Bukkit.getServer().getPlayer(args[0]) != null){
Also, you should always use floats
when setting health since a recent Bukkit update. setHealth(int)
is deprecated, and replaced with setHealth(float)
, so try:
targetPlayer.setHealth(20.0f);