Java switch：case表达式必须是常量表达式

Question

I have problem with the java switch im my school project: in code all constants in cases are underlined red and throw that case error

private static final int TCP = Integer.parseInt(PropertiesComunicator.getData("tcp"));
private static final int HTTP = Integer.parseInt(PropertiesComunicator.getData("http"));
private static final int HTTPS = Integer.parseInt(PropertiesComunicator.getData("https"));
private static final int TELNET = Integer.parseInt(PropertiesComunicator.getData("telnet"));
private static final int SSH = Integer.parseInt(PropertiesComunicator.getData("ssh"));
private static final int FTP_DATA = Integer.parseInt(PropertiesComunicator.getData("ftp-data"));
private static final int FTP_CONTROL = Integer.parseInt(PropertiesComunicator.getData("ftp-control"));

switch (portNumbers[i]) {

        case HTTP: 
                    portNames[i] = "http";
                    break;

        case HTTPS:
                    portNames[i] = "https";
                    break;

        case TELNET:
                    portNames[i] = "telnet";
                    break;

        case SSH: 
                    portNames[i] = "ssh";
                    break;

        case FTP_DATA:
                    portNames[i] = "ftp-data";
                    break;

        case FTP_CONTROL:
                    portNames[i] = "ftp-control";
                    break;

        default:
                    portNames[i] = null;
                    break;
        }

After a quick research on the internet i found that this error is because "case statements can only take compile-time constants, or enums" and my constant's values are taken from extern property file so i think this is the reason why this error occurs, but configuration of this constants by extern file is necessary condition for finishing my project :( Is there any solution except uncomfortable if-else recoding this part od source?

PS these few ports aren't the only i have to analyze...

Answer 1

gTypical approach here would be to use map/dictionary of some sort to map your input "keys" (in your case, portNumbers[i] ) to their "value" (eg map HTTP to "http").

You could do

Map<Integer, String> protos = new HashMap<Integer, String>();
protos.put(HTTP, "http");

and solve everything by using

portNames[i] = protos.get(portNumber[i]);