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Neal Gafter Releases First Java Closures Prototype

1 reply on 1 page. Most recent reply: Oct 31, 2007 8:09 AM by Daniel Jimenez

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Frank Sommers

Posts: 2642
Nickname: fsommers
Registered: Jan, 2002

Neal Gafter Releases First Java Closures Prototype Posted: Oct 30, 2007 11:57 AM
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Neal Gafter released the first prototype implementation of the closures proposal for Java 6.

Adding closures to the Java language is among the most hotly debated—and considered by many to be the most desirable—additions to Java since generic types were introduced three years ago. The proposal for Java closures has seen several competing versions, which converged to a single specification drafted by Neal Gafter and a group of experts in preparation for a JSR submission.

Neal Gafter has recently released an implementation of this proposal with the following features:

  • BGGA function type syntax
  • Closure literals
  • Closure conversion
  • The null type, disjunctive types, and exception transparency
  • Definite assignment
  • Unreachable and completion transparency.
  • Catching multiple exceptions at once like catch(X1|X2 ex) { ... [not closely related to closures but the implementation was simple once closures are there]

Missing from this implementation are :

  • A closure using a mutated variable from the enclosing scope
  • Nonlocal control-flow (break, return, and continue)
  • The control invocation statement and loop abstractions

What do you think of the closures proposal and the first prototype?

Daniel Jimenez

Posts: 40
Nickname: djimenez
Registered: Dec, 2004

Re: Neal Gafter Releases First Java Closures Prototype Posted: Oct 31, 2007 8:09 AM
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This is indeed exciting. Like Ricky (, I love playing around with the new syntax.

In addition to what's already there, and beyond the items the prototype doesn't yet support, there's two features I would be most interested in seeing.

One is mentioned by Neal himself: extension methods ( I for one have no problem stealing some of the great ideas coming from C#, and have lusted after this feature since I first heard of it.

The other is mentioned in comments: method reference syntax ( A quick review makes it seem like using an existing nested class vs a new anonymous class, but at the method level.

All in all, exciting changes are (hopefully) coming to Java!

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