public void insertUserData(String SQLiteName, String SQLiteSurname,
                           String SQLitePosition, double SQLiteSalary,
                           double SQLiteExperience) {
    try {
        sqlQuery = "INSERT INTO MainEmployeeData(Name, Surname, Position, Salary, Experience)" +
                "VALUES('" + SQLiteName + "', '" + SQLiteSurname + "', '" + SQLitePosition + "', " +
                "'" + SQLiteSalary + "', '" + SQLiteExperience + "')";

        boolSqlQuery = "SELECT Name, Surname " + "FROM MainEmployeeData WHERE Name = "" +
                SQLiteName + "" AND Surname = "" + SQLiteSurname + """;
        trueAnswer = "Data was successfully saved!";
        falseAnswer = "Record with such parameters already exists!";
        existenceCheckerInsertion(boolSqlQuery, sqlQuery, trueAnswer, falseAnswer);
    } catch (Exception e) {
        System.out.println(e.getMessage());
    }
}

public void deleteEmployeeData(String employeeName, String employeeSurname) {
    try {
        trueAnswer = "Data was successfully deleted!";
        falseAnswer = "No record with such parameters exists!";

        boolSqlQuery = "SELECT Name, Surname FROM MainEmployeeData WHERE Name = "" +
                employeeName + "" AND Surname = "" + employeeSurname + """;

        sqlQuery = "DELETE FROM MainEmployeeData WHERE Name = "" + employeeName + """ +
                "AND Surname = "" + employeeSurname + """;

        recordExistenceChecker(boolSqlQuery, sqlQuery, trueAnswer,
                falseAnswer);
    } catch (Exception e) {
        System.out.println(e.getMessage());
    }
}

public <E> void modifyEmployeeDataInDB(String getParameterToBeModified,
                                       E getOldParameter, E getNewParameter) {
    try {
        trueAnswer = "Data was successfully changed!";
        falseAnswer = "No record with such parameter found!";

        boolSqlQuery = "SELECT " + getParameterToBeModified + " FROM MainEmployeeData" +
                " WHERE " + getParameterToBeModified + " = " + """ + getOldParameter + """;

        sqlQuery = "UPDATE MainEmployeeData SET " + getParameterToBeModified +
                " = "" + getNewParameter + "" WHERE " + getParameterToBeModified +
                " = " + """ + getOldParameter + """;

        recordExistenceChecker(boolSqlQuery, sqlQuery, trueAnswer,
                falseAnswer);
    } catch (Exception e) {
        System.out.println(e.getMessage());
    }
}

private void recordExistenceChecker(String getBoolSqlQuery,
                                    String getSqlQuery,
                                    String getTrueAnswer,
                                    String getFalseAnswer) throws SQLException {
    stmt = connect.createStatement();
    stmt.execute(getBoolSqlQuery);

    ResultSet rs = stmt.getResultSet();

    if (rs.next()) {
        stmt.execute(getSqlQuery);
        System.out.print(getTrueAnswer);
        stmt.close();
    } else {
        System.out.println(getFalseAnswer);
    }

    stmt.close();
}

private void existenceCheckerInsertion(String getBoolSqlQuery,
                                       String getSqlQuery,
                                       String getTrueAnswer,
                                       String getFalseAnswer) throws SQLException {
    stmt = connect.createStatement();
    stmt.execute(getBoolSqlQuery);
    ResultSet rs = stmt.getResultSet();

    if (!rs.next()) {
        stmt.execute(getSqlQuery);
        System.out.print(getTrueAnswer);
        stmt.close();
    } else {
        System.out.println(getFalseAnswer);
    }

    stmt.close();
}