Country selector: if or ternary?

Question

String fileId = "CPP420.A2_2012072416244467745";        
String reg1 = "CPP350";        
String reg2 = "CPP420.A1";        
String reg3 = "CPP420.A2";        
String country = "";        
if(fileId.startsWith(reg1)) {        
    country = "CA";         
} else if(fileId.startsWith(reg2)) {        
    country = "US";         
} else if(fileId.startsWith(reg3)) {        
    country = "FR";        
} else {        
    System.out.println("Error invalid file");        
}  

OR

String country = fileId.startsWith(reg1) ? "CA" : "";
       country = fileId.startsWith(reg2) ? "US" : "";
       country = fileId.startsWith(reg3) ? "FR" : "";

if("".equals(country)) {
System.out.println("No country found");
}

Answer 1

Neither. Note: haven't tried this in and IDE, but you should be able to get the idea.

interface RegionID {
    boolean isRegionMatch(String fileID);
    String getRegionCode();
}

class SimpleMatchRegionID implements RegionID {
    private String regionPrefix;
    private String regionCode;

    public SimpleMatchRegionID(String regionPrefix, String regionCode) {
        this.regionPrefix = regionPrefix;
        this.regionCode = regionCode;
    }

    public boolean isRegionMatch(String fileID) {
        return fileID.startsWith(regeionPrefix);
    }

    public String getRegionCode() {
        return regionCode;
    }
}

RegionID us = new SimpleMatchRegionID("CPP420.A1", "US");
RegionID ca = new SimpleMatchRegionID("CPP350", "CA");
RegionID fr = new SimpleMatchRegionID("CPP350", "FR");
RegionID[] regions = {us, ca, fr};

public String findRegionCode(String fileID) {
    for (i = 0; i < regions.length; i++) {
        if (regions[i].isRegionMatch(fileID)) {
            return regions[i].getRegionCode();
        }
    }

    return "";
}

An implementation like this would allow you to load the regions array from a data file, or with some other run-time mechanism. It would also allow you to implement other strategies for recognizing a region that doesn't follow the same basic pattern.

Answer 2

You can improve the code even without a separate class in the case that you don't need other detection mechanisms. The following will allow you to easily add new prefixes but nothing more.

String fileId = "CPP420.A2_2012072416244467745";        
Map<String,String> countriesByPrefix = new HashMap<>() {{
    put("CPP350", "CA");
    put("CPP420.A1", "US");
    put("CPP420.A2", "FR");
}};
String country = null;
for (Map.Entry<String,String> entry : countriesByPrefix.entrySet()) {
    if (fileId.startsWith(entry.getKey()) {
        country = entry.getValue();
        break;
    }
}
if (country == null) {
    System.out.println("Error invalid file");
}

Answer 3

If you can use Java 7, you can put Strings in switch statements (this came with JSR334):

String fileId = "CPP420.A2_2012072416244467745";        
String country = "";  
String fileReg = fileId.split("_")[0];      
switch(fileReg) {
  case "CPP350" : country = "CA"; break;   
  case "CPP420.A1" : country = "US"; break;
  case "CPP420.A2" : country = "FR"; break;
  default : System.out.println("Error invalid file");    
}       

Answer 4

I already see some good/better solutions here but what I am missing is an example which uses the famous(?) java ENUM's

public enum Country {
    CA, US, FR;
}

public enum FileType {
    CPP350("CPP350", Country.CA),
    CPP420_A1("CPP420.A1", Country.US),
    CPP420_A2("CPP420.A2", Country.FR);

    private final String fileId;
    private final Country country;

    private FileType(final String fileId , final Country country) {
        this.fileId = fileId;
        this.country = country;
    }

    public Country getCountry() {
        return country;
    }

    public static FileType match( final String fileId ) {
        for ( final FileType fileType : values() ) {
            if ( fileId.startsWith( fileType.fileId ) ) {
                return fileType;
            }
        }
        return null;
    }
}

And the below code should help you to get your desired country for the given fileId.

final Country country = FileType.match( fileId ).getCountry();

Note: As you can see that there is a possibility for NullPointerException if no match found. But I believe it should be handled as part of the implementation.