public String convert(String in) {
int l = in.length();
StringBuffer out = new StringBuffer(l * 3);
char c;
for (int i = 0; i < l; ++i) {
 c = Character.toLowerCase(in.charAt(i));
 if (Character.isLetter(c)) {
  out.append(c - 96);
  out.append(' ');
 }
}
return out.toString();
}

Untested. And only works with ASCII data.

Johann

How about the following?
I suppose you want to economically convert a String into a BigInteger. If
economy is not your goal then there are other, more simple solutions.

import java.math.BigInteger;

// Enumerate in CHARSET all the characters to be used
 public String CHARSET = ". ABCDEFGHIJKLMNOPQRSTUVWXYZ???-1234567890,/&+'";

 public int NBROFCHARS = CHARSET.length();
 public BigInteger MULTIPLIER = new BigInteger("" + NBROFCHARS);

 private static BigInteger textToNumber(String text) {
   BigInteger result = BigInteger.ZERO;
   text = text.toUpperCase();
   for (int i = text.length() - 1; i >= 0; i--) {
     int place = CHARSET.indexOf("" + text.charAt(i));
     if (place < 0)
       place = 1;           // unknown replaced by a space because space is
2nd in CHARSET
     result = result.multiply(MULTIPLIER);
     BigInteger tobeadded = new BigInteger("" + place);
     result = result.add(tobeadded);
   }
   return result;
 }

And the reverse transformation, that is BigInteger to String :

 public String numberToString(BigInteger number)
 {
   StringBuffer text = new StringBuffer();
   while (number.compareTo(BigInteger.ZERO) > 0) {
     BigInteger[] b = number.divideAndRemainder(MULTIPLIER );
     number = b[0];
     int place= b[1].intValue();
     char c = CHARSET.charAt(place);
     text.append(c);
   }
   return text.toString();
 }

This is a fraction from a program. I made some changes, hope I got it all
right ...

Just curious, but why are you converting to the index of the characters
(plus one) in the alphabet?

String.toByteArray() will give you the characters as bytes, which you can
cast up to an int for each byte, but you'll also have to take 'a' from each
byte and add 1 in order to get the numbers you want.

And are you sure it's a string of numbers you want, and not an array?

w
a
z