public void connectToAndQueryDatabase(String username,String password){

    Connection con=DriverManager.getConnection(
        "jdbc:myDriver:myDatabase",
        username,
        password
    );

    Statement stmt=con.createStatement();
    ResultSet rs=stmt.executeQuery("SELECT a, b, c FROM Table1");

    while(rs.next()){
        int x=rs.getInt("a");
        String s=rs.getString("b");
        float f=rs.getFloat("c");
    }
}

Connection con=DriverManager.getConnection(
    "jdbc:postgresql://localhost:21500/test?user=fred&password=secret&ssl=true"
);

private static Connection getConnection(String url, java.util.Properties info, Class<?> caller) throws SQLException {
    ...

    // System 속성을 확인하여 초기 JDBC 드라이버 목록을 로드하고
    // 로드를 마치면 "JDBC DriverManager initialized" 메시지를 출력한다.
    ensureDriversInitialized();

    ...

    for (DriverInfo aDriver : registeredDrivers) {
      if (isDriverAllowed(aDriver.driver, callerCL)) {
        try {
            println("    trying " + aDriver.driver.getClass().getName());
            Connection con = aDriver.driver.connect(url, info);
            if (con != null) {
                // Success!
                println("getConnection returning " + aDriver.driver.getClass().getName());
                return (con);
            }
        } catch (SQLException ex) {
            if (reason == null) {
              reason = ex;
            }
        }

      } else {
        println("    skipping: " + aDriver.getClass().getName());
      }
    }
    
    ...
}

/**
 * A connection (session) with a specific database. 
 * SQL statements are executed and results are returned within the context of a connection.
 * ...
 */
public interface Connection extends Wrapper, AutoCloseable {
  Statement createStatement() throws SQLException;
  PreparedStatement prepareStatement(String sql)
      throws SQLException;
  DatabaseMetaData getMetaData() throws SQLException;
  
  void setAutoCommit(boolean autoCommit) throws SQLException;
  void commit() throws SQLException;
  void rollback() throws SQLException;
  void close() throws SQLException;
  ...
}

try (
    Connection connection = DriverManager.getConnection(
        "jdbc:mysql://localhost:3306/testdb",
        "testuser",
        "testpw" // 사용할 패스워드
    )
) {
    log.warn("####### connection = {}", connection);
    log.warn("####### Is connection closed? = {}", connection.isClosed());
    log.warn("####### url = {}", connection.getMetaData().getURL());
    log.warn("####### driverName = {}", connection.getMetaData().getDriverName());
    log.warn("####### databaseProductVersion = {}", connection.getMetaData().getDatabaseProductVersion());
    log.warn("####### userName = {}", connection.getMetaData().getUserName());
}

public interface Statement extends Wrapper, AutoCloseable {
  
  ResultSet executeQuery(String sql) throws SQLException;
  
  int executeUpdate(String sql) throws SQLException;
  
  boolean execute(String sql) throws SQLException; // 다른 오버로딩 메서드 존재
  ...
}

try (
    Connection connection = DriverManager.getConnection(~); // 위 Connection 생성 예시 참고
    Statement statement = connection.createStatement();
) {
    boolean result = statement.execute(createTableSql());
    log.warn("result = {}", result);
} catch (SQLException e) {
    log.warn("SQLException occurred > {}", e.getMessage());
}
...
private String createTableSql() {
    return "CREATE TABLE IF NOT EXISTS car"
    + "(car_no bigint unsigned not null primary key,"
    + "brand varchar(20) not null,"
    + "color varchar(20) not null)";
}

try (
    Connection connection = DriverManager.getConnection(~); // 위 Connection 생성 예시 참고
    Statement statement = connection.createStatement();
) {
    int result = statement.executeUpdate(insertCarSql());
    log.warn("result = {}", result);
} catch (SQLException e) {
    log.warn("SQLException occurred > {}", e.getMessage());
}
...
private String insertCarSql() {
    return "INSERT INTO car(car_no, brand, color)"
    + " VALUES(1, 'TESLA', 'BLUE')";
}

try (
    Connection connection = DriverManager.getConnection(~); // 위 Connection 생성 예시 참고
    Statement statement = connection.createStatement();
    ResultSet resultSet = statement.executeQuery("SELECT * FROM car");
) {
    log.warn("resultSet = {}", resultSet);
    
    // ResultSet에서 사용하는 cursor를 다음 row로 옮긴다. 
    // 여기에서는 첫 번째 row 밖에 없으므로 한 번만 실행되고 종료된다.
    while (resultSet.next()) {
      log.warn("car_no = {}",resultSet.getLong("car_no"));
      log.warn("brand = {}",resultSet.getString("brand"));
      log.warn("color = {}",resultSet.getString("color"));
    }
} catch (SQLException e) {
    log.warn("SQLException occurred > {}", e.getMessage());
}

try (
    Connection connection = DriverManager.getConnection(~); // 위 Connection 생성 예시 참고
    PreparedStatement preparedStatement = connection.prepareStatement(updateCarSql());
) {
    // 매개변수 값 설정
    preparedStatement.setString(1, "RED");
    preparedStatement.setLong(2, 1L);

    // 명령문 실행
    int result = preparedStatement.executeUpdate();
    log.warn("result = {}", result); // 1

} catch (SQLException e) {
    log.warn("SQLException occurred > {}", e.getMessage());
}
...
private String updateCarSql() {
    return "UPDATE car SET color=? WHERE car_no=?";
}

try (
    Connection connection = DriverManager.getConnection(~); // 위 Connection 생성 예시 참고
    CallableStatement callableStatement = connection.prepareCall(insertCarCallableSql());
) {
    // output 매개변수 설정
    callableStatement.registerOutParameter(1, Types.BIGINT); // 프로시저의 output 매개변수 등록
    
    // input 매개변수 설정
    callableStatement.setLong(2, 2L); // car_no가 1인 row는 이미 있으므로 2L로 설정
    callableStatement.setString(3, "TESLA");
    callableStatement.setString(4, "WHITE");
    
    // 명령문 실행
    callableStatement.execute();
    
    int result = callableStatement.getInt(1);
    log.warn("result = {}", result); // lastInsertId에 해당하는 2 출력
        
} catch (SQLException e) {
    log.warn("SQLException occurred > {}", e.getMessage());
}
...
private String insertCarCallableSql() {
    return "{call insertCar(?,?,?,?)}";
}

String updateBrandSql = "UPDATE car SET brand=? WHERE car_no=?";
String updateColorSql = "UPDATE car SET color=? WHERE car_no=?";

try (
    Connection connection = DriverManager.getConnection(~); // 위 Connection 생성 예시 참고
        
    PreparedStatement pstmtForUpdateBrand = connection.prepareStatement(updateBrandSql);
    PreparedStatement pstmtForUpdateColor = connection.prepareStatement(updateColorSql);
) {
    // 브랜드 변경
    pstmtForUpdateBrand.setString(1, "GENESIS");
    pstmtForUpdateBrand.setLong(2, 2L);

    // 색상 변경
    pstmtForUpdateColor.setString(1, "BLACK");
    pstmtForUpdateColor.setLong(2, 2L);

    boolean autoCommit = connection.getAutoCommit();
    try {
        connection.setAutoCommit(false);
    
        // 명령문 실행
        pstmtForUpdateBrand.executeUpdate();
        pstmtForUpdateColor.executeUpdate();
    
        // 트랜잭션 커밋
        connection.commit();
    } catch (SQLException e) {
        log.warn("SQLException occurred > {}", e.getMessage());
        connection.rollback();
    } finally {
        connection.setAutoCommit(autoCommit);
    }
        
} catch (SQLException e) {
    log.warn("SQLException occurred > {}", e.getMessage());
}

connection.close();