title: HashSet contains duplicate entries
body: <p>A HashSet only stores values ones, when the equals method says that they're the same. Thats what I thought.</p>
  
  <p>But now i'm adding Elements to a HashSet where the equals method returns true and the size of the set still grows?? sorry I'm confused. Some hints where i'm wrong would be nice.</p>
  
  <pre><code>Element t1 = new Element(false, false, false, false);
  Element t2 = new Element(true, true, true, true);
  Element t3 = new Element(false, false, false, false);
  
  if (t1.equals(t3))
      System.out.println("they're equal");
  
  Set&lt;Element&gt; set = new HashSet&lt;&gt;();
  
  set.add(t1);
  set.add(t2);
  set.add(t3);
  
  System.out.println("set size: " + set.size());
  </code></pre>
  
  <p>so in this example my console output is:</p>
  
  <blockquote>
    <p>they're equal<br>
    set size: 3</p>
  </blockquote>
  
  <p>That makes no sense to me.. shouldn the size be 2?</p>