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?