Comments on: Hashtable Collisions and String Hashcode http://www.shankh.com/2010/05/13/hashtable-collisions-and-string-hashcode/ Where you search Begins... Thu, 12 Jan 2012 19:28:25 +0000 hourly 1 http://wordpress.org/?v=3.3.1 By: admin http://www.shankh.com/2010/05/13/hashtable-collisions-and-string-hashcode/comment-page-1/#comment-7480 admin Sun, 09 Jan 2011 12:42:12 +0000 http://www.shankh.com/?p=159#comment-7480 @hixxxxx . You are absolutely correct. System.identityHashcode is not guaranteed to produce unique hashcodes and in a 64 bit system there is high chance of collisions. One has to implement a proper equals method to maintain hashtable data integrity. My example was just to explain hashtable collisions and I made it clear that people should use the proper way of equals implementation as mentioned here http://www.ibm.com/developerworks/java/library/j-jtp05273.html @hixxxxx . You are absolutely correct. System.identityHashcode is not guaranteed to produce unique hashcodes and in a 64 bit system there is high chance of collisions. One has to implement a proper equals method to maintain hashtable data integrity. My example was just to explain hashtable collisions and I made it clear that people should use the proper way of equals implementation as mentioned here http://www.ibm.com/developerworks/java/library/j-jtp05273.html

]]> By: hixxxxx http://www.shankh.com/2010/05/13/hashtable-collisions-and-string-hashcode/comment-page-1/#comment-5772 hixxxxx Thu, 02 Dec 2010 10:23:14 +0000 http://www.shankh.com/?p=159#comment-5772 Hi, your implementation with the hashcode= System.identityHashCode(this); is still combersome! identityHashCode(this), which falls back to Object.hashCode is still a hashcode and may collide (to different Objects (here: key1 & key2) can have the same hashcode! This is rare but happens if you deal with loads of data). Since your equals method does not look into a value, but only operates with the hashcode, you would get a problem when you deal with several tens of thousands of objects (it might be, that on 64bit systems where the object pointer is a long collisions become extremly rare, but there is no guaranty for that!) Best g Hi,

your implementation with the hashcode= System.identityHashCode(this); is still combersome! identityHashCode(this), which falls back to Object.hashCode is still a hashcode and may collide (to different Objects (here: key1 & key2) can have the same hashcode! This is rare but happens if you deal with loads of data). Since your equals method does not look into a value, but only operates with the hashcode, you would get a problem when you deal with several tens of thousands of objects (it might be, that on 64bit systems where the object pointer is a long collisions become extremly rare, but there is no guaranty for that!)

Best
g

]]> By: admin http://www.shankh.com/2010/05/13/hashtable-collisions-and-string-hashcode/comment-page-1/#comment-1717 admin Fri, 14 May 2010 16:13:16 +0000 http://www.shankh.com/?p=159#comment-1717 Program updated and entry rewritten. As usual your comments are welcome Program updated and entry rewritten. As usual your comments are welcome

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