Methode Error Calculations Class

package laurenshup.supercalculator;

import org.bukkit.Bukkit;
import org.bukkit.entity.Player;
import org.bukkit.plugin.Plugin;

public class Calculations {

	Plugin plugin;

	public double Calc3Arguments() {

		for(Player player : Bukkit.getOnlinePlayers()) {
			String playercheck = plugin.getConfig().getString("players." + player.getUniqueId() + ".lastchatcalc.out");
			if(playercheck == "needed") {
				String a1s = plugin.getConfig().getString("players." + player.getUniqueId() + "lastchatcalc.arguments.a1").replace("stack", "64");double a1 = Integer.parseInt(a1s);
				String a2s = plugin.getConfig().getString("players." + player.getUniqueId() + "lastchatcalc.arguments.a2").replace("stack", "64");double a2 = Integer.parseInt(a2s);
				String a3s = plugin.getConfig().getString("players." + player.getUniqueId() + "lastchatcalc.arguments.a3").replace("stack", "64");double a3 = Integer.parseInt(a3s);
				if(a1s.equals("(") && a3s.equals(")")) {
					return a2;
				} else {
					if(a2s.equals("+")) {double out = a1 + a3;return out;}
					if(a2s.equals("-")) {double out = a1 - a3;return out;}
					if(a2s.equals("*")) {double out = a1 * a3;return out;}
					if(a2s.equals("/")) {double out = a1 / a3;return out;}
				}
			}
		}
		return 00.00;
	}

}