How to convert an alphanumeric phone number to digits

Question

UPDATE:

The final version of my utility looks like this:

StringBuilder b = new StringBuilder();

for(char c : inLetters.toLowerCase().toCharArray())
{
    switch(c)
    {
    case '0':                                          b.append("0"); break;
    case '1':                                          b.append("1"); break;
    case '2': case 'a': case 'b': case 'c':            b.append("2"); break;
    case '3': case 'd': case 'e': case 'f':            b.append("3"); break;
    case '4': case 'g': case 'h': case 'i':            b.append("4"); break;
    case '5': case 'j': case 'k': case 'l':            b.append("5"); break;
    case '6': case 'm': case 'n': case 'o':            b.append("6"); break;
    case '7': case 'p': case 'q': case 'r': case 's':  b.append("7"); break;
    case '8': case 't': case 'u': case 'v':            b.append("8"); break;
    case '9': case 'w': case 'x': case 'y': case 'z':  b.append("9"); break;
    }
}

return builder.toString();

---

ORIGINAL QUESTION:

I'm taking on the simple task of converting an alphanumeric phone number to a string of digits. For example, 1-800-HI-HAXOR would become 1-800-44-42967. My initial attempt was to create a nasty switch statement, but I'd love a more elegant, and efficient solution. Here's what I've got:

for(char c : inLetters.toLowerCase().toCharArray())
{
    switch(c)
    {
    case '0':                                         result+="0"; break;
    case '1':                                         result+="1"; break;
    case '2': case 'a': case 'b': case 'c':           result+="2"; break;
    case '3': case 'd': case 'e': case 'f':           result+="3"; break;
    case '4': case 'g': case 'h': case 'i':           result+="4"; break;
    case '5': case 'j': case 'k': case 'l':           result+="5"; break;
    case '6': case 'm': case 'n': case 'o':           result+="6"; break;
    case '7': case 'p': case 'q': case 'r': case 's': result+="7"; break;
    case '8': case 't': case 'u': case 'v':           result+="8"; break;
    case '9': case 'w': case 'x': case 'y': case 'z': result+="9"; break;
    }
}

Thanks!

Answer 1

The switch statement is not really that bad. Your algorithm is linear with respect to the length of the phone number. The code is readable and pretty easy to verify by inspection. I wouldn't mess with it, except to add a default case for handling errors. (I'm not a Java programmer, so forgive me if it's called something else.)

If you have to make it faster, a pre-initialized table indexed by character would avoid any comparisons beyond basic error checking. You could even avoid the case conversion by duplicating the values in the table (digit['A'] = digit['a'] = "2";). The cost of initializing the table would be amortized over the total number of conversions.