title: How to generate a random number that is unique each time
body: <p>Hey I am trying to create a program that generates a random number that is only allowed to be used once. Sorry if that's confusing I'll try to explain. I want to have a program generate numbers from 1-100, but say if it generates 33, then for the rest of the number generation process 33 cannot be generated again, So I should end with exactly 100 different numbers. Any help is really appreciated, Thank you.</p>
  
  <p>Here's my attempt so far</p>
  
  <pre><code>public class Seed {
  
      public static void main(String[] args) {
          // TODO Auto-generated method stub
          int a =0; 
          for (int i =0; i &lt;20;i++) {
               a = (int) Math.ceil(10 * Math.random())  ;
              System.out.println(a);
              int x = a;
              System.out.println("This is x: " + x);
  
              if (x == a )
              {
                  a = (int) Math.ceil(10 * Math.random())  ;
              }
          }
      }
  }
  </code></pre>