title: How to find total number of different items within an arraylist.
body: <p>I've done some searching but I wasn't able to find a valid solution. I have an arraylist storing Strings such as gum, socks, OJ, dog food...</p>
  
  <p>I am having trouble iterating the list to determine the total number of differnt types of items.</p>
  
  <p>ie.</p>
  
  <pre><code>ArrayList&lt;String&gt; Store = new ArrayList&lt;String&gt;();
      this.Store.add("Gum");
      this.Store.add("Gum");
      this.Store.add("Socks");
      this.Store.add("Candy");
  </code></pre>
  
  <p>The list has 4 total items, but only three different kinds of items (Gum, Sucks, Candy).</p>
  
  <p>How would I design a method to calculate the 3?</p>