java evolution of eclipse collections – live blogging from qcon

The Java Evolution of Eclipse Collections
Speaker: Kristen O’Leary
See the list of all blog posts from the conference

Eclipse Collections

  • was once GS (Goldman Sachs) Collections
  • Memory efficient collections framework
  • Open sourced in 2012

Java 8

  • 8.0 compatible with Java 8+
  • Extend Java 8 Functional Interfaces
  • New APIs – ex: reduceInPlace


  • RichIteratable.detectWith() used to rutn null if no match
  • Pre Java-8 could use detectIfNone() to create if doesn’t exist
  • New method detectWithOptional() which returns Optional wrapper


  • Collectors2 has collectors
  • Can collect into Bag, ImmutableSet, BiMap, Stack, etc
  • Have full primitive collections library
  • Have full set of multi-map (map with multiple values for same key ex: key to list/set)
  • Have extra APIs like chunk() and zip()

Default methods

  • RichIterable is common interface so default methods helpful.
  • Used to add reduceInPlace() so don’t need to stream and create new collection
  • Also useful for asLazy() or toImutabile() since Eclipse Collections doesn’t provide stream() there.

Primitive Collections

  • Code generate the primitive classes so symmetry
  • Showed impressive memry savings – Eclipse Collections and Trove equivalent. Much smaller than with autoboxing and faster too
  • LazyIterable availalbe for all 8 primitive types. Just call asLazy(). A LazyIterabe can be reused unlike a stream.

Java 9

  • Module system
  • Internal API Encapsulation
  • Need to change APIs that use reflection in order to build. Can’t call setAccessible(true) any more.
  • There is a command line argument to ignore reflection errors. Don’t want to impose that on callers

I like that Kristen uses kata examples to show hw the APIs work.

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