Playground Bukkit Plugin

import org.bukkit.plugin.java.JavaPlugin;
import org.bukkit.command.Command;
import org.bukkit.command.CommandSender;
import org.bukkit.entity.Player;

public class main extends JavaPlugin{

    @Override
    public void onEnable() {
        getLogger().info("Playground Plugin has been enabled!");
    }

    @Override
    public void onDisable() {
        getLogger().info("Playground Plugin has been disabled!");
    }

    public boolean onCommand(CommandSender sender, Command cmd, String label, String[] args) {

        if(cmd.getName().equalsIgnoreCase("playground") && sender instanceof Player) {
            Player player = (Player) sender;
            player.sendMessage("This plugin is working correctly.");
            return true;
        }

        return false;

    }
}