title: Good way to store unique integers
body: <p><strong>My Question Is:</strong> What's a fast way to determine whether a number is contained in a <code>Collection</code> to know whether to add it to the collection and maintain uniqueness. I would rather not iterate through the list if I can help it. </p>
  
  <p>I have a <code>List&lt;Integer&gt;</code> called <code>numberList</code>. I want it to store unique integers and never allow duplicates to be added. I would like to do something like this:</p>
  
  <pre><code>private void add(int number) {
    if (!numberList.contains(number)) {
      numberList.add(number);
    }
  }
  </code></pre>
  
  <p>But obviously this wont work because <code>numberList</code> contains a list of <code>Integer</code> objects so regardless of the number each is a unique object.</p>
  
  <p>Thanks!</p>