As adding closures to the Java language is increasingly becoming a reality, many developers started to have second thoughts about extending Java with closures. The debate seems to center not around the specifics of any one closures syntax, but whether Java needs any language additions on the scale of closures at all.

In a recent blog post, On Closures, Tim Bray summarizes key arguments of this debate, and highlights why he thinks Java became so successful despite the language's shortcomings:

I started out nervous with the idea of adding closures to Java, and I think I’ve slid firmly into the “contra” camp. One reason is that it seems increasingly a bad idea to add anything to the Java language...

Java worked so well because it hit the 80/20 point; for my money one of the loudest, cleanest 80/20 technology victories ever. Subsequent attempts to fill in the 20% were, well, mostly harmless. Until generics, which are a disaster; they have made Java harder to learn and to understand, and you can’t avoid them...

So I’m really scared about trying to chip away any further at whatever’s left of the 20%. Also, I look at the motivating examples for closures and I think that the conventional alternatives aren’t that bad. Also, I look at the proposed code and I think that on balance it’ll make Java harder to read. Also, as Bharath points out, if you really need closures and and functional-programming goo and suchlike, there are at least two excellent Java-platform languages that have elegant, well-tested designs: Scala and JRuby.

Bray's point is that Java's open-sourcing has raised the bar for any new technology or proposal desiring to become a core part of the language:

Now that Java is Open-Source, anyone can go cook up whatever loony closure facility they want, and if it’s good enough, people will start using it whether the binary build has “Java” stamped on the outside or not, and then start shouting that it should be in the standard distro, and only then should the JCP consider going near this tar-pit.

Bray also points out that since the JVM is now open-source, making the VM more hospitable to languages that already have elegant closures facilities may be wiser approach than extending the Java language:

My favorite place to start improving Java wouldn’t be with the language at all, it’d be the Multi-Language VM project. The motivating use-cases for that aren’t theoretical in the slightest, they have names and addresses and are screaming for love.

To what extent do you think should Java incorporate new language features? Do you support adding closures to Java?

class Foo<E extends Foo<E>> {
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}