public enum USER_COLUMN {
    ID("id"),
    USERNAME("username"),
    PASSWORD("password"),

    private final String name;
    USER_COLUMN(String name) {this.name = name;}

    @Override
    public String toString() {
        return name;
    }
}

private void addColumnToSelect(USER_COLUMN col) {
    addColumnToSelect(col.toString());
}

private void addColumnToSelect(GENDER_COLUMN col) {
    addColumnToSelect(col.toString());
}

private void addColumnToSelect(ROLE_COLUMN col) { // Role is an other table
    addColumnToSelect(col.toString());
}

private void addColumnToSelect(String col_name) {...}