### Question:
Util { public static String hexStringToBinaryString(String s) { StringBuilder sb = new StringBuilder(); for(int i=0;i<s.length();i++) { char c = s.charAt(i); int index=0; if(c >= '0' && c <= '9') { index = c - '0'; } else if(c >= 'a' && c <= 'f') { index = c - 'a' + 10; } else if(c >= 'A' && c <= 'F') { index = c - 'A' + 10; } else { return null; } sb.append(binary[index]); } return sb.toString(); }  static String byteToHexString(byte b); static byte[] hexStringToByteArray(String s); static String byteArrayToHexString(byte[] raw, boolean spaces); static String hexStringToBinaryString(String s); static String intToHexString(int i); static int hexStringToInt(String s);  }### Answer:
@Test public void testHexStringToBinaryString() { System.out.println("hexStringToBinaryString"); String s = "FF124A"; String expResult = "111111110001001001001010"; String result = Util.hexStringToBinaryString(s); assertEquals(expResult, result); }