JDK-8023463 : Improvements to HashMap/LinkedHashMap use of bins/buckets and trees (red/black)
  • Type: Bug
  • Component: core-libs
  • Sub-Component: java.util:collections
  • Affected Version: 8
  • Priority: P2
  • Status: Closed
  • Resolution: Fixed
  • Submitted: 2013-08-21
  • Updated: 2013-10-14
  • Resolved: 2013-09-04
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JDK 8
8 b108Fixed
Related Reports
Blocks :  
JDK-8024009 - Remove jdk.map.useRandomSeed system property
Relates :  
JDK-8005698 - Handle Frequent HashMap Collisions with Balanced Trees
Relates :  
JDK-8023795 - java/lang/reflect/Generics/Probe.java needs update for api changes
Description
Update HashMap and LinkedHashMap using similar techniques from ConcurrentHashMap where normally bins/buckets are used to store entries. When the bin size gets over a threshold the bin is converted to a red/black tree, which reduces the complexity when looking up entries for keys that hash to the same value.
Comments
HashMap has already been updated to use tree bins like CHM, this work was done as part of JEP-180 (http://openjdk.java.net/jeps/180). During the review/discussion there were ideas and improvements suggested that Doug has implemented. In addition there was follow-up discussion that conclusion that the hash seed wasn't useful and should be removed.
21-08-2013