Right Output but not passing task requirements

Question about the task

Under discussion

The output I get from this code is correct, but it isn't passing the task requirements (specifically the first two). Why do I keep on having this issue? Please help.

The public static toHex(String) method must convert the string representation of a binary number, received as an input parameter, from the binary numeral system to hexadecimal and return its string representation.
And conversely, the public static toBinary(String) method converts from the string representation of a hexadecimal number to the string representation of a binary number.

The methods only work with non-empty strings.
If the input parameter is an empty string or null, then both methods return an empty string.
If the input parameter of the toHex(String) method contains any character other than 0 or 1, then the method returns an empty string.
If the input parameter of the toBinary(String) method contains any character other than digits from 0 to 9 or lowercase Latin letters from a to f, then the method returns an empty string.

Your task is to implement these methods.

One algorithm for converting the string representation of a binary number to the string representation of a hexadecimal number is as follows:

We check the length of the string received in the input parameter. It must be a multiple of 4.
If this is not the case, then add the required number of 0s to the beginning of the string.
We take every four characters (bits) and check which hexadecimal character they correspond to.

For example:

the binary representation is "100111010000", where "1001" is "9", "1101" is "d", and "0000" - "0"
the hexadecimal representation is "9d0".

One algorithm for converting the string representation of a hexadecimal number to the string representationof a binary number is as follows:
We take each character and check which binary number (4 bits) it corresponds to.

For example:

the hexadecimal representation is "9d0", where "9" is "1001", "d" is "1101", and "0" is "0000"
the binary representation is "100111010000".

The main() method is not involved in testing.

Requirements:

The toHex(String) method needs to be implemented as outlined in the task conditions.
The toBinary(String) method needs to be implemented as outlined in the task conditions.
The Integer.toBinaryString(int) and Long.toBinaryString(int) methods cannot be used.
The Integer.toHexString(int) and Long.toHexString(int) methods cannot be used.
The Integer.parseInt(String, int) and Long.parseLong(String, int) methods cannot be used.
The Integer.toString(int, int) and Long.toString(long, int) methods cannot be used.
You cannot use a BigInteger object.
You cannot use a BigDecimal object.

package en.codegym.task.pro.task09.task0908; /* Binary to hexadecimal converter */ public class Solution { public static void main(String[] args) { String binaryNumber = "100111010000"; System.out.println("Binary number " + binaryNumber + " is equal to hexadecimal number " + toHex(binaryNumber)); String hexNumber = "9d0"; System.out.println("Hexadecimal number " + hexNumber + " is equal to binary number " + toBinary(hexNumber)); } public static String toHex(String binaryNumber) { if (binaryNumber == null || binaryNumber.isEmpty()){ return ""; } StringBuilder hexNumber = new StringBuilder(); for (int i = binaryNumber.length(); i >= 0; i -=4){ int endIndex = i; int startIndex = Math.max(0, i - 4); String binaryGroup = binaryNumber.substring(startIndex, endIndex); hexNumber.insert(0, binarytoHex(binaryGroup)); } return hexNumber.toString(); } public static String toBinary(String hexNumber) { if (hexNumber == null || hexNumber.isEmpty()){ return ""; } StringBuilder binaryNumber = new StringBuilder(); for (int i = 0; i < hexNumber.length(); i++){ char hexDigit = hexNumber.charAt(i); binaryNumber.append(hexToBinary(hexDigit)); } return binaryNumber.toString(); } // helper method to convert a 4-digit binary group to a hexadecimal digit public static char binarytoHex(String binaryGroup){ if (binaryGroup.equals("0000")) return '0'; else if (binaryGroup.equals("0001")) return '1'; else if (binaryGroup.equals("0010")) return '2'; else if (binaryGroup.equals("0011")) return '3'; else if (binaryGroup.equals("0100")) return '4'; else if (binaryGroup.equals("0101")) return '5'; else if (binaryGroup.equals("0110")) return '6'; else if (binaryGroup.equals("0111")) return '7'; else if (binaryGroup.equals("1000")) return '8'; else if (binaryGroup.equals("1001")) return '9'; else if (binaryGroup.equals("1010")) return 'A'; else if (binaryGroup.equals("1011")) return 'B'; else if (binaryGroup.equals("1100")) return 'C'; else if (binaryGroup.equals("1101")) return 'D'; else if (binaryGroup.equals("1110")) return 'E'; else if (binaryGroup.equals("1111")) return 'F'; else return '0'; // Default to '0' if not a valid binary group } //helper method to convert a hexadecimal digit to 4-digit binary public static String hexToBinary(char hexDigit){ switch (hexDigit) { case '0': return "0000"; case '1': return "0001"; case '2': return "0010"; case '3': return "0011"; case '4': return "0100"; case '5': return "0101"; case '6': return "0110"; case '7': return "0111"; case '8': return "1000"; case '9': return "1001"; case 'A': return "1010"; case 'B': return "1011"; case 'C': return "1100"; case 'D': return "1101"; case 'E': return "1110"; case 'F': return "1111"; default: return "0000"; // Default to '0000' if not a valid hexadecimal digit } } }

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Guadalupe Gagnon

Level 37 , Tampa, United States

28 October 2023, 00:43

Output is not correct:

String binaryNumber = "1001110100001";
System.out.println("Binary number " + binaryNumber + " is equal to hexadecimal number " + toHex(binaryNumber));
String hexNumber = "3A1";
System.out.println("Hexadecimal number " + hexNumber + " is equal to binary number " + toBinary(hexNumber));

The output with this test code is: Binary number 1001110100001 is equal to hexadecimal number 03A1 Hexadecimal number 3A1 is equal to binary number 001110100001 So if "1001110100001" equals 03A1 (there also should not be any preceding 0) then when passing "3A1" to the toBinary() method should result in the same thing.

Guadalupe Gagnon

Level 37 , Tampa, United States

28 October 2023, 00:48

The toBinary() method in your code is arriving at the correct results (other than the preceding zeros). Your toHex() method is not. The correct hex of "1001110100001" is "13A1".