// Generating random hex String up to 16 characters long

private static Random wheel = new Random(); // seed with time of day

// ...

/* Note there is no such method as Random.nextLong( long ),
 * so you have to trim the result to 0..Long.MAX_VALUE yourself.
 */

/* To get numeric strings with  digits 0-9 try this: */
String almostUniqueAndRandom = Long.toString( wheel.nextLong() & Long.MAX_VALUE );

/* generate random hex Strings of form
 * "0" .. "7fffffffffffffff", a maximum 16 characters long.
 * representing 0..Long.MAX_VALUE
 * To get strings with letters a-f and digits 0-9 try this:
 */
String almostUniqueAndRandom = Long.toHexString( wheel.nextLong() & Long.MAX_VALUE );

/* To get strings with letters a-z and digits 0-9 try this: */
String almostUniqueAndRandom = Long.toString( wheel.nextLong() & Long.MAX_VALUE , 36 );