Java: convert binary string to hex string [duplicate]

Answer 1

Instead of Long.toHexString I would use Long.parseLong to parse the value and then String.format to output the value with the desired width (21 in your example):

public static String binaryToHex(String bin) {
   return String.format("%21X", Long.parseLong(bin,2)) ;
}

Answer 2

Just add the zeros manually. Here's one way:

public static String binaryToHex(String bin){
    return ("0000000000000000" + Long.toHexString(Long.parseLong(bin, 2)).replaceAll(".*.{16}", "$1");
}

Answer 3

Not very elegant, but works

public static String binaryToHex(String bin) {
    String hex = Long.toHexString(Long.parseLong(bin, 2));
    return String.format("%" + (int)(Math.ceil(bin.length() / 4.0)) + "s", hex).replace(' ', '0');
}

I've used String.format() to left pad string with whitespaces then called replace() to replace it with zeros.