title: Are there any unordered, repeatable Collection classes in Java?
body: <p>I want a collection contains unordered, repeatable items.
  In Java, Set is unrepeatable, List is ordered, which are not what I want.</p>
  
  <p>It seems Pool is an appropriate collection, but it doesn't exist in Java.
  The interface should be as following:</p>
  
  <pre><code>public interface Pool&lt;T&gt; {
      void set(T item);
      T get();
  }
  </code></pre>
  
  <p>Does it exist somewhere?</p>
  
  <hr>
  
  <p><strong>Complementing：</strong></p>
  
  <p>I realize that I expressed my thought incorrectly. Infact, I want to have an interface like this:</p>
  
  <pre><code>public interface Pool&lt;T&gt; {
      void put(T item);
      T randomRemove();
  }
  </code></pre>
  
  <p>That is to say, I want to get an item ramdomly everytime. How can I achieve it?</p>