private static String[] getFrequencies(String resolution, DisplayMode[] modes) {
        List<String> freqs = new ArrayList<>(4);
        for (DisplayMode mode : modes) {
            String res = mode.getWidth() + " x " + mode.getHeight();
            String freq;
            if (mode.getRefreshRate() == DisplayMode.REFRESH_RATE_UNKNOWN) {
                freq = "???";
            } else {
                freq = mode.getRefreshRate() + " Hz";
            }
            if (res.equals(resolution) && !freqs.contains(freq)) {
                freqs.add(freq);
            }
        }

        return freqs.toArray(new String[0]);
    }
Returns every possible refresh rate for the given resolution.
jme3-awt-dialogs/src/main/java/com/jme3/awt/AWTSettingsDialog.java