Convert Binary Output File to Hex Equivalent

binaryStringtoHex.java

import java.io.*;

private static void convertFileOutputToHex(String fileName) throws IOException {

        ArrayList<String> programLines = new ArrayList<>();
        try {
            FileReader fr = new FileReader(fileName);
            BufferedReader br = new BufferedReader(fr);
            while (br.ready()) {
                programLines.add(br.readLine());
            }
        } catch (IOException e) {
            System.out.println("Error - Cannot find binary string input file.");
        }

        FileWriter fw = new FileWriter("prog.hex");
        for (String line : programLines) {

            // Pad with leading 0's until
            while((line.length() % 4) != 0){
                line = "0" + line;
            }

            // Convert binary digits to hex 4 at a time.
            String hexStringToPrint = "";
            for(int n = 0; n < line.length(); n = n + 4){

                // Construct quadlet
               String quadlet = String.valueOf(line.charAt(n + 0)) + String.valueOf(line.charAt(n + 1))
                                + String.valueOf(line.charAt(n + 2)) + String.valueOf(line.charAt(n + 3));

               hexStringToPrint = hexStringToPrint + convertBinaryToHex(quadlet);
            }

            fw.write(hexStringToPrint);
            fw.write("\n");
        }
        fw.close();
    }

    private static String convertBinaryToHex(String binaryQuad){

        Map<String, String> hexLookUpTable = new HashMap<>();

        hexLookUpTable.put("0000", "0");
        hexLookUpTable.put("0001", "1");
        hexLookUpTable.put("0010", "2");
        hexLookUpTable.put("0011", "3");
        hexLookUpTable.put("0100", "4");
        hexLookUpTable.put("0101", "5");
        hexLookUpTable.put("0110", "6");
        hexLookUpTable.put("0111", "7");
        hexLookUpTable.put("1000", "8");
        hexLookUpTable.put("1001", "9");
        hexLookUpTable.put("1010", "A");
        hexLookUpTable.put("1011", "B");
        hexLookUpTable.put("1100", "C");
        hexLookUpTable.put("1101", "D");
        hexLookUpTable.put("1110", "E");
        hexLookUpTable.put("1111", "F");

        return hexLookUpTable.get(binaryQuad);
    }