В чём проблема?
package com.javarush.task.pro.task09.task0908;
import java.util.regex.Pattern;
/*
Двоично-шестнадцатеричный конвертер
*/
public class Solution {
private static final String HEX = "0123456789abcdef";
public static void main(String[] args) {
String binaryNumber = "100111010000";
System.out.println("Двоичное число " + binaryNumber + " равно шестнадцатеричному числу " + toHex(binaryNumber));
String hexNumber = "9d0";
System.out.println("Шестнадцатеричное число " + hexNumber + " равно двоичному числу " + toBinary(hexNumber));
}
public static String toHex(String binaryNumber) {
String hexNumber = "";
int decimalNumber = 0;
if (binaryNumber == null || binaryNumber.equals("") || !binaryNumber.matches("[10]+")) {
return "";
}
while (binaryNumber.length() % 4 != 0) {
binaryNumber = "0" + binaryNumber;
}
for (int i = 0; i < binaryNumber.length(); i++) {
decimalNumber = decimalNumber + Character.getNumericValue(binaryNumber.charAt(binaryNumber.length() - 1 - i)) * (int) Math.pow(2, i);
}
while (decimalNumber != 0) {
hexNumber = HEX.charAt(decimalNumber % 16) + hexNumber;
decimalNumber = decimalNumber / 16;
}
return hexNumber;
}
public static String toBinary(String hexNumber) {
int decimalNumber = 0;
String binaryNumber = "";
if (hexNumber == null || hexNumber.equals("") || !hexNumber.matches("[0-9a-fA-F]+")) {
return "";
}
for (int i = 0; i < hexNumber.length(); i++) {
char ch = hexNumber.charAt(i);
int indexElement = HEX.indexOf(ch);
decimalNumber = 16 * decimalNumber + indexElement;
}
while (decimalNumber != 0) {
binaryNumber = decimalNumber % 2 + binaryNumber;
decimalNumber = decimalNumber / 2;
}
return binaryNumber;
}
}