[hardwired]

Code:

String str = "9,10,11,12";
String isIn = " ";
do {
    isIn = JOptionPane.showInputDialog("Please enter a number");
    if(isIn == null) break;

    int x = str.indexOf(isIn);

    boolean confirmed = false;
    if(x != -1) {
        boolean hasLeadingComma = x > 0 && str.charAt(x-1) == ',';
        boolean hasTrailingComma = x < str.lastIndexOf(",") &&
            str.charAt(x + isIn.length()) == ',';
        boolean isFirst = x == 0 && hasTrailingComma;
        boolean isLast = x > str.lastIndexOf(",") && hasLeadingComma;
        confirmed = isFirst || isLast ||
            (hasLeadingComma && hasTrailingComma);
    }

    if(confirmed) {
        System.out.println("Found " + isIn + " at index " + x);
    } else {
        System.out.println(isIn + " not found, x = " + x);
    }
} while(isIn.length() > 0);