patternList.setCellFactory(TextFieldListCell.forListView(new StringConverter<Pattern>() {
    @Override
    public String toString(Pattern pattern) {
        return pattern.toString();
    }

    @Override
    public Pattern fromString(String string) {
        try {
            return Pattern.compile(string);
        } catch (PatternSyntaxException e) {
            return null;
        }
    }
}));
patternList.setOnEditCommit(e -> {
    if (e.getNewValue() == null) {
        // TODO pattern syntax error, prevent commit and stay in edit mode
    } else {
        patternList.getItems().set(e.getIndex(), e.getNewValue());
    }
});