java - ArrayList contains -

i don't understand what's happening, if explain me great.

so, here's code:

public static arraylist<integer> numbers = new arraylist<integer>();  public static void main(string[] args){     for(int =0; != 90; i++){         system.out.println(generate());     } }  public static int generate(){     random random = new random();     int rand = random.nextint(89)+1;      while(numbers.contains(rand)){ //<---here seems problem         rand = random.nextint(89)+1;         system.out.println("number: " + rand + " exists!");     }     numbers.add(rand);     return rand; } 

i writing program generates random number 0-90, each of different last. unfortunately, seems while loop returns true.

you can using collections shuffle

public static arraylist<integer> numbers = new arraylist<integer>(); for(int =1; <= 90; i++){     number.add(i) } collections.shuffle(numbers); // @ point number shuffled. 

read shuffle.