MySql class in Java

package sql;

import java.sql.*;
import java.util.ArrayList;

public class MySql {

    private String host;
    private int port;
    private String username;
    private String password;
    private String database;

    private Connection con;
    private Statement st;
    private ResultSet rs;

    public MySql()
    {
        this.host ="localhost";
        this.port = 3306;
        this.username = "";
        this.password = "";
        this.database = "";
        this.OpenConnection();
    }

    public void OpenConnection()
    {
        try {
            con = DriverManager.getConnection("jdbc:mysql://" + this.host + ":" + this.port + "/" + this.database + "?user=" + this.username + "&password=" + this.password + "&serverTimezone=UTC");
            st = con.createStatement();
        } catch(Exception ex) {
            System.out.println("ERROR: "+ex);
        }
    }

    public ResultSet query(String query)
    {
        try {
            st = con.prepareStatement(query);
            rs = st.executeQuery(query);
            return rs;
        } catch(Exception e) {
            e.printStackTrace();
        }
        return null;
    }

    public ArrayList<String> sqla(String query)
    {
        ResultSet result = query(query);

        ArrayList<String> array = new ArrayList<>();

        if( !result.beforeFirst() )
        {
            return array;
        }

        while(result.next()))
        {

        }
    }

    public int insert(String table, String cond)
    {
        String query = "INSERT INTO " + table + " " + cond;

        try {
            st = con.createStatement();
            return st.executeUpdate(query);
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return 0;
    }

    public int update(String table, String cond)
    {
        String query = "UPDATE " + table + "SET " + cond;
        try {
            st = con.createStatement();
            return st.executeUpdate(query);
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return 0;
    }

    public int delete(String table, String cond)
    {
        String query = "DELETE FROM " + table + " " + cond;

        try {
            st = con.createStatement();
            return st.executeUpdate(query);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return 0;
    }

}