How to convert a UPC-E barcode to a UPC-A barcode?

Question

What is the algorithm for converting a zero-suppressed, eight-digit GTIN-12 identifier (represented as a UPC-E barcode) into the full, twelve-digit version as shown in a UPC

Answer 1

This duplicates the algorithm in @Terry Burton's answer, written in Java.

switch (data.charAt(6)) {
    case '0':
    case '1':
    case '2': {
        data = data.substring(0, 3) + "0000" + data.charAt(6) + data.substring(3, 6) + data.charAt(7);
        break;
    }
    case '3': {
        data = data.substring(0, 4) + "00000" + data.substring(4, 5) + data.charAt(7);
        break;
    }
    case '4': {
        data = data.substring(0, 5) + "00000" + data.charAt(5) + data.charAt(7);
        break;
    }
    case '5':
    case '6':
    case '7':
    case '8':
    case '9': {
        data = data.substring(0, 6) + "0000" + data.charAt(6) + data.charAt(7);
        break;
    }
}