Selected/non selected items color with geotools map example

Question

I've taken the Geotools example for showing map data. There is a function setting a color (yellow) for selected items. The function sets the rest of the items to a default color even though the layer has another defined color. I would like to have the color unchanged for the not-selected items, but the yellow color for the selected items. How can I change the code to keep the original color setting while setting yellow for the selected items? See example:

public void displaySelectedFeatures(Set<FeatureId> IDs) {
    Style style;

    if (IDs.isEmpty()) {
        style = createDefaultStyle();

    } else {
        style = createSelectedStyle(IDs);
    }

    Layer layer = mapFrame.getMapContent().layers().get(0);
    ((FeatureLayer) layer).setStyle(style);
    mapFrame.getMapPane().repaint();
}
private Style createDefaultStyle() {
    Rule rule = createRule(LINE_COLOUR, FILL_COLOUR);

    FeatureTypeStyle fts = sf.createFeatureTypeStyle();
    fts.rules().add(rule);

    Style style = sf.createStyle();
    style.featureTypeStyles().add(fts);
    return style;
}

private Style createSelectedStyle(Set<FeatureId> IDs) {
    Rule selectedRule = createRule(SELECTED_COLOUR, SELECTED_COLOUR);
    selectedRule.setFilter(ff.id(IDs));
    Rule otherRule = createRule(LINE_COLOUR, FILL_COLOUR);
    otherRule.setElseFilter(true);
    FeatureTypeStyle fts = sf.createFeatureTypeStyle();
    fts.rules().add(selectedRule);
    fts.rules().add(otherRule);
    Style style = sf.createStyle();
    style.featureTypeStyles().add(fts);
    return style;
}

Answer 1

The code as shown in your question should work fine, unless you are changing the LINE_COLOR and FILL_COLOR variables between calls. But you could store the default rule in a field and then reuse it as the else rule in the selection. So something like this should work:

Rule rule = createRule(LINE_COLOUR, FILL_COLOUR);
private Style createDefaultStyle() {
    rule.setElseFilter(false); // it's the only rule here
    FeatureTypeStyle fts = sf.createFeatureTypeStyle();
    fts.rules().add(rule);

    Style style = sf.createStyle();
    style.featureTypeStyles().add(fts);
    return style;
}

private Style createSelectedStyle(Set<FeatureId> IDs) {
    Rule selectedRule = createRule(SELECTED_COLOUR, SELECTED_COLOUR);
    selectedRule.setFilter(ff.id(IDs));

    rule.setElseFilter(true); // only match the non-selected features
    FeatureTypeStyle fts = sf.createFeatureTypeStyle();
    fts.rules().add(selectedRule);
    fts.rules().add(otherRule);
    Style style = sf.createStyle();
    style.featureTypeStyles().add(fts);
    return style;
}