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BigInteger x = new BigInteger ("530500452766");
byte // convert x to a String
byte[] byteArray = x.toByteArray(); // convert to byte array
String s = new String(byteArray);    // s prints as "{,J?z" -
                                     // the fourth character is invalid

// convert s back to a BigInteger
byteArray = s.getBytes();       // convert to bytes
x = new BigInteger(byteArray);  // now x = 530500435870

When run on a platform where the default character encoding is US-ASCII, the string s gets the value {{{J}}, because some of the characters are unprintable. When converted back to a BigInteger, x gets the value 149830058370101340468658109.

Compliant Solution

This compliant solution first produces a String representation of the BigInteger object, and then converts the String object to a byte array. This process is reversed on input. Because the textual representation in the String object was generated by the BigInteger class, it contains valid characters.

BigInteger x = new BigInteger ("530500452766");
String s = x.toString();  // valid character data

try {
  byte[] byteArray = s.getBytes("UTF8");
  String ns = new String(byteArray, "UTF8");  // ns prints as "530500452766"

  BigInteger x1 = new BigInteger(ns);        // construct the original BigInteger
} catch (UnsupportedEncodingException ex) {
  // handle error
}

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