public class MaterialInHandCommand implements CommandExecutor {
 public Beam plugin;
 public MaterialInHandCommand(Beam plugin){
 this.plugin = plugin;
 this.plugin.getCommand("materialinhand").setExecutor(this);
 }

 @Override
 public boolean onCommand(CommandSender commandSender, Command command, String s, String[] strings) {
 if(!(commandSender instanceof Player)){
 commandSender.sendMessage("Only players can execute this command");
 return true;
 }
 Player p = (Player) commandSender;
 p.sendMessage(p.getInventory().getItemInMainHand().getType().name());

 return false;
 }
}