Main :
package Coins;

import org.bukkit.plugin.java.JavaPlugin;

public class Main extends JavaPlugin {

	@Override
	public void onEnable() {
		MySQL.connect();
		MySQL.createTable();
		CoinAPI.setCoins("test", 10);
	}
	public void onDisable() {
		MySQL.disconnect();
	}
}
CoinAPI:
package Coins;

import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

import org.bukkit.entity.Player;

public class CoinAPI {

	public static int getCoins(String uuid) {
		try {
			PreparedStatement st = MySQL.con.prepareStatement("SELECT coins FROM coinTable WHERE UUID = ?");
			st.setString(1, uuid);
			ResultSet rs = st.executeQuery();
			while (rs.next()) {
				return rs.getInt("coins");
			}


		} catch (SQLException e) {
			e.printStackTrace();
		}
		return -1;
	}
	public static void setCoins(String uuid, int coins) {
		if(getCoins(uuid) == 1) {
			try {
				PreparedStatement st = MySQL.con.prepareStatement("INSERT INTO coinTable (UUID,coins) VALUES (?,?)");
				st.setString(1, uuid);
				st.setInt(2, coins);
				st.executeUpdate();
			} catch (SQLException e) {
				e.printStackTrace();
			}
		} else {
			PreparedStatement st;
			try {
				st = MySQL.con.prepareStatement("UPDATE coinTable SET coins = ? WHERE UUID = ?");
				st.setString(2, uuid);
				st.setInt(1, coins);
				st.executeUpdate();
			} catch (SQLException e) {
				e.printStackTrace();
			}

		}
	}
	public  static void addCoins(String uuid, int coins) {

		setCoins(uuid, coins + getCoins(uuid));
	}
	public static void removeCoins(String uuid, int coins) {
		setCoins(uuid, getCoins(uuid) - coins);
	}
}
MySQL:
package Coins;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;



public class MySQL {

	public static Connection con;
	public static String passvd = "m9TM3RfpLkeRfJdKbqtu";
	public static String database = "KontanexCoins";
	public static String user = "root";
	public static String host = "localhost";
	public static int port = 3306;


	public static void connect() {
		if(!isConnected()) {
			try {
				con = DriverManager.getConnection("jdbc:mysql://" + host + ":" + port + "/" + database, user, passvd);
				System.out.println("§aMySQL Verbunden!");
			} catch (SQLException e) {
				e.printStackTrace();
			}
		}
	}
	public static void disconnect() {
		if (isConnected()) {
			try {
				con.close();
				System.out.println("§aMySQL verbindung getrennt!");
			} catch (SQLException e) {
				e.printStackTrace();
			}
		}

	}
	public static boolean isConnected() {
		return (con != null);
	}
	public static void createTable() {
		try {
			con.prepareStatement("CREATE TABLE IF NOT EXISTS coinTable (UUID VARCHAR (100), UUID VARCHAR (100), coins INT (16))").executeUpdate();
		} catch (SQLException e) {
			e.printStackTrace();
		}
	}
}