Closures in Java 7

Question

I have heard that closures could be introduced in the next Java standard that is scheduled to be released somewhere around next summer.

What would this syntax look like?

I read somewhere that introducing closures in java is a bigger change than generic was in java 5. Is this true? pros and cons?

(By now we definitely know that closures not will be included in the next Java release)

OR

edit: http://puredanger.com/tech/2009/11/18/closures-after-all/ :D

edit2: Re-thinking JDK7: http://blogs.sun.com/mr/entry/rethinking_jdk7

Answer 1

Have a look at http://www.javac.info/ .

It seems like this is how it would look:

boolean even = { int x => x % 2 == 0 }.invoke(15);

where the { int x => x % 2 == 0 } bit is the closure.

Answer 2

It really depends on what gets introduced, and indeed whether it will be introduced at all. There are a number of closure proposals of varying sizes.

See Alex Miller's Java 7 page for the proposals and various blog posts.

Personally I'd love to see closures - they're beautiful and incredibly helpful - but I fear that some of the proposals are pretty hairy.

Answer 3

This is the java 7 features http://tech.puredanger.com/java7/#switch the examples are very usefull.

Answer 4

Note that a "function-type" is really a type under the proposal:

{int => boolean} evaluateInt;    //declare variable of "function" type
evaluateInt = {int x => x % 2 }; //assignment

Answer 5

I think there is still a lot of debate going in with regards to what syntax will ultimately be used. I'd actually be pretty surprised if this does make it into Java 7 due to all of that.

Answer 6

In November 2009 there was a surprising u-turn on this issue, and closures will now be added to Java 7.

Answer 7

Closures have some serious edge cases. I would say that Closures are a much more significant change than Generics and the later still has a number hairy edge cases. e.g. The Java Collections libraries cannot be written/compiled without warnings.

Answer 8

Unofortunately you will not find closure in Java 7. If you are looking for a lighter solution to have closure in java just now check out the lambdaj project:

http://code.google.com/p/lambdaj/

Update: Java 7 will actually have closures.

Answer 9

closures will be annoyinglly verbose if there won't be any sort of type inference... :(