Decimal to any base

There is the interview question that asks you to convert decimal to hexadecimal. And it prompt me to write some code about converting decimal to any bases.

public class DecimalToOtherBase {
 public static String decimalToHex(int n){
     StringBuilder sb = new StringBuilder();
     while(n > 0){
      int resi = n % 16;
      if(resi >= 10)
       sb.insert(0, (char)('A' + resi - 10));
      else
       sb.insert(0, resi);
         n /= 16;
     }
     return sb.length() == 0 ? "0" : sb.toString();
 }
 public static int HexToDecimal(String s){
  if(s == null)
   throw new IllegalArgumentException("Null string");
  int num = 0;
  int pow = 1;
  for(int i = s.length() - 1; i >= 0; i--){
   char c = s.charAt(i);
   num += (Character.isLetter(c) ? (c - 'A' + 10) : (c - '0')) * pow;
   pow *= 16;
  }
  return num;
 }
 public static String DecToAnyBase(int n, int base){
  if(n < 10)
   return DecToAnyBaseSmaller(n, base);
  else if(n > 10)
   return DecToAnyBaseGreater(n, base);
  return String.valueOf(n);
 }
 /**
  * base 2 - 9
  * @param n
  * @param base
  * @return
  */
 private static String DecToAnyBaseSmaller(int n, int base){
  StringBuilder sb = new StringBuilder();
     while(n > 0){
      int resi = n % base;
      sb.insert(0, resi);
         n /= base;
     }
     return sb.length() == 0 ? "0" : sb.toString();
 }
 /**
  * base must be less than 36
  * @param n
  * @param base
  * @return
  */
 private static String DecToAnyBaseGreater(int n, int base){
     StringBuilder sb = new StringBuilder();
     while(n > 0){
      int resi = n % base;
      if(resi >= 10)
       sb.insert(0, (char)('A' + resi - 10));
      else
       sb.insert(0, resi);
         n /= base;
     }
     return sb.length() == 0 ? "0" : sb.toString();
 }

 public static void main(String[] args) {
  System.out.println(decimalToHex(127));
  System.out.println(DecToAnyBase(25, 16));
  System.out.println(HexToDecimal("7F"));

 }

}

Moreover, LeetCode has two problems basically ask you to convert decimal to 26 base and vice versa. See this and this blog.