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Sequential Alphanumeric IDs
public class AlphanumericIdUtil {
private static final String VALID_CHARACTERS = "23456789abcdefghjkmnpqrstuvwxyz";
public static void main(String[] args) {
* Go from number (like 12345) to alphanumeric ID (like a8e7z4)
* @param number The number you wish to convert to ID
* @return the alphanumeric ID as a string
public static String getIdFromNumber(Integer number) {
// The magic number we're trying to get down to 0
long magicNumber = number;
// Some placeholder values
long wholeNum = 0;
int remainder = 0;
String id = "";
// The value we'll use as our modulo, just stored in a variable because it's simpler
int modVal = VALID_CHARACTERS.length();
// Loop until the magic number (AKA the whole number) is not zero (>0 also works)
while (magicNumber != 0) {
// First, take the magic number, divide it by the modulo value, and store that as our whole
// number
wholeNum = (long) Math.floor(magicNumber / modVal);
// Next, find the remainder of when we take the magic number and divide it by the modulo value
remainder = (int) magicNumber % modVal;
// Then, take the remainder that we just got, find what position it is in our valid
// characters, and store it in our ID (yes, this means the ID is backwards, but we fix that
// later)
id += VALID_CHARACTERS.charAt(remainder);
// Lastly, make the magic number the whole number from above (since we don't need to deal with
// the remainder)
magicNumber = wholeNum;
// Loop again until the whole num is zero!
// One last thing: reverse the string. StringBuilder has a nice reverse method, so that's what
// I'm using to reverse the string.
return new StringBuilder(id).reverse().toString();
* Go from alphanumeric ID (like a8e7z4) to number (like 12345)
* @param id The string with the alphanumeric ID
* @return The number as an int
public static Integer getNumberFromId(String id) {
// A placeholder for the base 10 number
Integer base10Number = 0;
// Loop over each character in the input string
for (int i = 0; i < id.length(); i++) {
// Get the "current" character
char c = id.charAt(i);
// Find where that character is in the list of valid characters
// TODO: What do we do if it's not in that list?
int index = VALID_CHARACTERS.indexOf(c);
// Check if the character was able to be found
if (index == -1) {
throw new IllegalArgumentException("Character \"" + c
+ "\" is not a valid character. The only valid characters are: " + VALID_CHARACTERS);
// Take the base (31) to the power of the total number of characters, minus i, minus 1, and
// mutiply it by the index
base10Number += (int) Math.pow(VALID_CHARACTERS.length(), id.length() - i - 1) * index;
return base10Number;
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