static int number(char c)
    {
        switch (c)
        {
            case 'a':
                return 1;
            case 'b':
                return 2;
            case 'c':
                return 3;
            case 'd':
                return 4;
            case 'e':
                return 5;
            case 'f':
                return 6;
            case 'g':
                return 7;
            case 'h':
                return 8;
            case 'i':
                return 9;
            case 'j':
                return 10;
            case 'k':
                return 11;
            case 'l':
                return 12;
            case 'm':
                return 13;
            case 'n':
                return 14;
            case 'o':
                return 15;
            case 'p':
                return 16;
            case 'q':
                return 17;
            case 'r':
                return 18;
            case 's':
                return 19;
            case 't':
                return 20;
            case 'u':
                return 21;
            case 'v':
                return ID_ENUM_SET;
            case 'x':
                return ID_ENUM;
            case 'y':
                return ID_COLLECTION;
            default:
                return 0;
        }
    }
Used when the type is an interface (Collection/List/Set/SortedSet).

@author David Yu
@created Apr 24, 2012
protostuff-runtime/src/main/java/io/protostuff/runtime/PolymorphicCollectionSchema.java