title: Treeset.contains() problem
body: <p>So I've been struggling with a problem for a while now, figured I might as well ask for help here.</p>
  
  <p>I'm adding Ticket objects to a TreeSet, Ticket implements Comparable and has overridden equals(), hashCode() and CompareTo() methods. I need to check if an object is already in the TreeSet using contains(). Now after adding 2 elements to the set it all checks out fine, yet after adding a third it gets messed up.</p>
  
  <p>running this little piece of code after adding a third element to the TreeSet, Ticket temp2 is the object I'm checking for(verkoopLijst).</p>
  
  <pre><code>    Ticket temp2 = new Ticket(boeking, TicketType.STANDAARD, 1,1);
      System.out.println(verkoop.getVerkoopLijst().first().hashCode());
      System.out.println(temp2.hashCode());
  
      System.out.println(verkoop.getVerkoopLijst().first().equals(temp2));
      System.out.println(verkoop.getVerkoopLijst().first().compareTo(temp2));
      System.out.println(verkoop.getVerkoopLijst().contains(temp2));
  </code></pre>
  
  <p>returns this:</p>
  
  <pre><code>22106622
  22106622
  true
  0
  false
  </code></pre>
  
  <p>Now my question would be how this is even possible?</p>
  
  <p>Edit:</p>
  
  <pre><code>public class Ticket implements Comparable{
  
      private int rijNr, stoelNr;
      private TicketType ticketType;
      private Boeking boeking;
  
  
      public Ticket(Boeking boeking, TicketType ticketType, int rijNr, int stoelNr){    
          //setters
      }
  
      @Override
      public int hashCode(){
          return boeking.getBoekingDatum().hashCode();     
      }
  
      @Override
      @SuppressWarnings("EqualsWhichDoesntCheckParameterClass")    
      public boolean equals(Object o){
         Ticket t = (Ticket) o;
  
         if(this.boeking.equals(t.getBoeking())
                 &amp;&amp;
            this.rijNr == t.getRijNr() &amp;&amp;  this.stoelNr == t.getStoelNr()
                 &amp;&amp;
            this.ticketType.equals(t.getTicketType()))
         {
             return true;
         }
  
         else return false;
  
      }
  
      /*I adjusted compareTo this way because I need to make sure there are no duplicate Tickets in my treeset. Treeset seems to call CompareTo() to check for equality before adding an object to the set, instead of equals().
  
  
       */
      @Override
      public int compareTo(Object o) {
          int output = 0;
          if (boeking.compareTo(((Ticket) o).getBoeking())==0)
          {
              if(this.equals(o))
              {
                  return output;
              }
              else return 1;
          }
          else output = boeking.compareTo(((Ticket) o).getBoeking());
          return output;
      }
  
      //Getters &amp; Setters
  </code></pre>