random generator for unique numbers

Arielis's Avatar, Join Date: Jul 2008
Newbie Member
I have an issue ,trying to build a unique number generator.
Specifiacally, the generator is this
                Random randomPerson=new Random(System.nanoTime());
		int no_persons=persons.length;
		int cnt=0;
		while(cnt<70) {
			int person=randomPerson.nextInt(no_persons);
			if(function()) {
function() returns a boolean whether the random number hasn't used before (and some other operations eg insertion to an array)
When this program is executed, I either take the aprropriate output, or the program stucks (infinite loop). Is there any possibility to fix this infinite loop?

Thanks in advace!
oogabooga's Avatar
Ambitious contributor
Presumably you mean something like this:
bool is_unique( int n) {
    // check array

int get_unique_person() {
    Random randomPerson = new Random( System.nanoTime());
    int no_persons = persons.length;
    int max_tries = 70;
    int cnt, person;

    for( cnt = 0; cnt < max_tries; ++cnt) {
        person = randomPerson.nextInt( no_persons);
        if( is_unique( person)) break;  // exit loop if it IS unique
    if( cnt == max_tries) { // No unique number found in max_tries.
        // Deal with it....
    return person;
If the range of your random numbers is relatively small, and particularly if you need to use most or all of them, then a better solution might be to create your own class called RndUnique that would contain a shuffled array of the integers in the range and return them one at a time.

Last edited by oogabooga; 6Oct2008 at 23:01.. Reason: fixed scope of "person"
Arielis's Avatar, Join Date: Jul 2008
Newbie Member