面向 Java 开发人员的 Scala 指南

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本文为Java开发者提供Scala编程入门指南，通过实例展示了Scala如何简化代码、提高清晰度，特别关注类操作和面向对象的函数编程，提供从Hello World到更复杂应用的实践案例。

http://www.ibm.com/developerworks/cn/java/j-scala01228.html
Chapter1 面向 Java 开发人员的 Scala 指南: 面向对象的函数编程
some code
So, for instance, the already mentioned Array class has a function, filter, which is defined in Listing 7:

Listing 7. Partial listing of Array.scala

class Array[A]
{
    // ...
  	def filter  (p : (A) => Boolean) : Array[A] = ... // not shown
}

Listing 7 declares that p is a function that takes a parameter of the generic type specified by A and returns a boolean. The Scala documentation states that filter "Returns an array consisting of all elements of this array that satisfy the predicate p." This means that if I want to go back to my Hello World program for a moment and find all the command-line arguments that start with the letter "G," writing it is as simple as Listing 8:

Listing 8. Hello, G-men!

object HelloWorld
{
  def main(args: Array[String]): Unit = {
    args.filter( (arg:String) => arg.startsWith("G") )
        .foreach( (arg:String) => Console.println("Found " + arg) )
  }
}

Here, filter takes the predicate, an anonymous function that implicitly returns a boolean (the result of the startsWith() call) and calls the predicate with every element in the "args" array. If the predicate returns true, it adds it to the results array. After walking through the entire array, it takes the results array and returns it, which is immediately then used as the source for a "foreach" call, which does exactly as it implies: foreach takes another function and applies that function to every element in the array (in this case, to simply display each one).
It's not too hard to imagine what the Java equivalent to HelloG.scala above would look like, and it's not too hard to recognize that the Scala version is much, much shorter, and a lot clearer, too.

Chapter 3
面向 Java 开发人员的 Scala 指南: 类操作
http://www.ibm.com/developerworks/cn/java/j-scala02198.html#resources