Scala advantages after Java having closures [close

With closures being added to Java, what is Scala's advantage over Java as a language choice?

Can someone elaborate on any advantages?

回答1:

Apart from closures (which Java doesn't appear all that close to having), here's a list of features in Scala that are missing from Java. I'll omit libraries here and concentrate on the features of the language itself. This is not comprehensive by any means, but I think it contains the big ticket items.

Implicit parameters / conversions
Pattern matching, case classes
Type inferencing (some)
Higher-kinded types (abstraction over type constructors)
Monadic for comprehensions
Variance annotations
Interfaces with behavior (traits)
Default and named arguments
Unified methods and operators (methods can be used as infix operators, operators can be overloaded because they're just methods)
Unified type hierarchy; no primitive types
Properties rather than getters and setters
Abstract values
First-class immutable references (vals are as easy to declare as vars)
By-name (lazy) terms (maybe Java closures would make this reasonably easy to express)
Some tail-call recursion optimization
Abstract types
Type aliasing
Self types
Path-dependent types
Structural types
Type ascription, as distinguished from type casting
Renaming imports
First-class modules (objects)
First-class packages
Reified generics (manifests)
Delimited continuations

Some cool secondary constructs that these building blocks enable:

Type classes (via implicit parameters and higher-kinded types)
The "Pimp My Library" pattern (via implicit conversions)
Internal DSLs (via operator overloading and infix methods)
Parser combinators (enabled by higher-order functions and made pretty by infix methods)
Generators, coroutines, custom control structures (via delimited continuations)
Type-level programming (via higher-kinded and abstract types)
Obsolescence of dependency injection frameworks (via the Cake Pattern)

Lastly, I'll mention that Scala has a REPL (read-evaluate-print-loop)--not really a feature of the language itself, but it's very nice to have!

回答2:

Even if Java 7 [8,..] will have first-class functions one day, it still lacks for implicits, type inference, powerful Collections library, pattern matching, traits and lots of other things boosting productivity. Not talking about various Actor libraries, rich capabilities of building DSLs,...

回答3:

The latest I've heard is that closures won't make it into Java 7.

http://www.baptiste-wicht.com/2010/09/jdk-7-features-updated-plan-b-is-apparently-here/

http://openjdk.java.net/projects/jdk7/features/

The second link clearly lists project Lambda (closures) as deferred to JDK 8.