package jdbc;

import java.sql.*;
import static java.lang.System.*;

public class MySqlDb
{
    private Connection connection;
    private Statement statement;

    public MySqlDb(String url, String dbName, String username, String password)
            throws SQLException {

            connection = DriverManager.getConnection(
                            "jdbc:mysql://" + url + ":3306/" + dbName,
                             username,
                             password);
    }

    public String select(String tableName, String fields[]) {
        return select(tableName, fields, "1 = 1");
    }

    public String select(String tableName, String fields[], String crits) {
        String selectStatement = "SELECT * "
                               + "FROM " + tableName + " "
                               + "WHERE " + crits;
        String ret = "";

        try {
            statement = connection.createStatement();
            ResultSet result = statement.executeQuery(selectStatement);

            while (result.next()) {
                for (String field : fields) {
                    String currentFieldValue = result.getString(field);

                    if (currentFieldValue != null) {
                        ret += result.getString(field) + "t";
                    }
                }

                ret = ret.substring(0, ret.length() - 1) + "n";
            }

        } catch (SQLException e) {
            err.println(createSqlExceptionInfo(e));
        } finally {
            resetStatement();
        }

        return ret;
    }

    public void insert(String sqlInsert) {
        try {
            statement = connection.createStatement();

            statement.executeUpdate(sqlInsert);
        } catch (SQLException e) {
            err.println(createSqlExceptionInfo(e));
        } finally {
            resetStatement();
        }
    }

    public void update(String sqlUpdate) {
        try {
            statement = connection.createStatement();

            statement.executeUpdate(sqlUpdate);
        } catch (SQLException e) {
            err.println(createSqlExceptionInfo(e));
        } finally {
            resetStatement();
        }
    }

    public void delete(String sqlDelete) {
        try {
            statement = connection.createStatement();

            statement.executeUpdate(sqlDelete);
        } catch (SQLException e) {
            err.println(createSqlExceptionInfo(e));
        } finally {
            resetStatement();
        }
    }

    public boolean closeConnection() {
        try {
            connection.close();

            return true;
        } catch (SQLException e) {
            err.println(createSqlExceptionInfo(e));
        }

        return false;
    }

    public static String createSqlExceptionInfo(SQLException e) {
        String ret   = "SQL-State:t"            + e.getSQLState()  + "n";
        ret         += "SQL error-code:t"       + e.getErrorCode() + "n";
        ret         += "Description:t"          + e.getMessage();

        return ret;
    }

    private void resetStatement() {
        if (statement != null) {
            statement = null;
        }
    }
}

package jdbc;

import static java.lang.System.*;
import java.sql.SQLException;

public class Jdbc
{
    public static void main(String[] args)
    {
        MySqlDb mysql = null;

        try {
            mysql = new MySqlDb("localhost", "seminar_db", "root", "root");
        } catch (SQLException e) {
            MySqlDb.createSqlExceptionInfo(e);
        }

       if (mysql != null) {

            mysql.insert(
                "INSERT INTO Seminar (thema, beschreibung) " +
                    "VALUES ('Java', "
                        + "'Introduction to Java.')");
            mysql.insert(
                "INSERT INTO Seminar (thema, beschreibung) " +
                    "VALUES ('Java 2', "
                        + "'Advanced Java.')");
            mysql.insert(
                "INSERT INTO Seminar (thema, beschreibung) " +
                    "VALUES ('PHP', "
                        + "'Get started with PHP.')");
            mysql.insert(
                "INSERT INTO Seminar (thema, beschreibung) " +
                    "VALUES ('XML', "
                        + "'XML-Introduction.')");
            mysql.insert(
                "INSERT INTO Seminar (thema, beschreibung) " +
                    "VALUES ('HTML/CSS', "
                        + "'Webdesign course')");
            mysql.insert(
                "INSERT INTO Seminar (thema, beschreibung) " +
                    "VALUES ('JavaScript', "
                        + "'Webprogramming')");
       }

       String[] fields = new String[2];
       fields[0] = "thema";
       fields[1] = "beschreibung";

       out.println(mysql.select("Seminar", fields));

       mysql
        .update(
            "UPDATE Seminar SET beschreibung = 'PHP beginner' WHERE thema = 'PHP'"
        );

       out.println(mysql.select("Seminar", fields, "thema = 'PHP'"));

       if (mysql.closeConnection() == true) {
           out.println("Database connection has been closed.");
       }
    }
}

Java    Introduction to Java.
Java 2  Advanced Java.
PHP Get started with PHP.
XML XML-Introduction.
HTML/CSS    Webdesign course
JavaScript  Webprogramming

PHP PHP beginner

Database connection has been closed.
BUILD SUCCESSFUL (total time: 0 seconds)