How to split a String into a sunstring and number

How can I split a string"KD-435" into two substrings to check whether the first substring "KD-"begins with the following characters"KD-" and the second substring is number beteewn "400-500". I have the following method and I want to change it to do that at this position "if (ssid.startsWith("KD-"))"

        private void check_wifi_available() {
                WifiManager wifiManager = (WifiManager) this
                                .getSystemService(this.WIFI_SERVICE);

                final List<ScanResult> results = wifiManager.getScanResults();
                if (results != null) {

                        List<ScanResult> updatedResults = new ArrayList<ScanResult>();
                        // pick wifi access ponits which begins with these "KD" characters.
                        for (int i = 0; i < results.size(); i++) {
                                String ssid = results.get(i).SSID;
                                if (ssid.startsWith("KD-")) {

                                        updatedResults.add(results.get(i));
                                }
                        }
                        if (updatedResults.size() > 0) {
                                String a = calculateBestAccessPoint(updatedResults);
                                textWifi.setText(a.toString());
                        }
                }
        }