Re: Sort Map on Value

From:
Tom Anderson <twic@urchin.earth.li>
Newsgroups:
comp.lang.java.programmer
Date:
Wed, 26 Aug 2009 21:50:23 +0100
Message-ID:
<alpine.DEB.1.10.0908262141260.23001@urchin.earth.li>
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On Wed, 26 Aug 2009, Wojtek wrote:

Lew wrote :

Wojtek wrote:

?@Override
?public boolean equals( Object key )
?{
? ?return ivKey.equals( ((PersonMapKey) key).getKey() );
?}

?@Override
?public int compareTo( PersonMapKey personKey )
?{
? ?return ivName.compareTo( personKey.getName() );
?}


Lew wrote:

Is this consistent with 'equals()'?


Wojtek wrote:

No, it is consistent with compareTo() as per the interface.


There is more than one interface involved, here. You need to be
specific.


Well the compareTo() is from the interface, the hashCode() and equals() are
overriding Object methods.


From java.lang.Comparable:

  The natural ordering for a class C is said to be consistent with equals
  if and only if e1.compareTo(e2) == 0 has the same boolean value as
  e1.equals(e2) for every e1 and e2 of class C.

If you have John Smith 1 and John Smith 2, then equals will say no, but
compareTo will say yes, the above invariant will be false, and Doug Lea
will be very, very cross with you. Furious.

tom

--
Our only chance for survival is better engineering. -- James Dyson
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