Java和Scala容器的转换

http://docs.scala-lang.org/zh-cn/overviews/collections/conversions-between-java-
and-scala-collections

import scala.collection.JavaConversions._

scala convert int to long

参考http://stackoverflow.com/questions/19647525/how-to-convert-any-a-number-to-a-long

val number:AnyVal = 10

val l:Long = number.asInstanceOf[Number].longValue

直接用asInstanceOf[Long]会报错。

scala split("|")的问题

参考http://stackoverflow.com/questions/28173414/scala-string-split-works-incorrectly

split("|")的结果是分成了char，正确的写法应该是split("\\|")

Scala格式化数字输出

".3f".format(1.23456)  // 1.234

import java.text.DecimalFormat
val formatter = new DecimalFormat("#.###")
formatter.format(1)  // 1
formatter.format(1.34)  // 1.34
formatter.format(4.toFloat / 3)  // 1.333

IntelliJ IDEA分别搭建基于maven和sbt的Scala项目

About the settings and keyboard shortcuts in IntelliJ, please see this doc.

About how to build Spark apps in IntelliJ, please see this doc.

Scala中this.type的使用

一直有一个疑问没搞懂，有必要在这里发上一帖，参见我提的问题和回答：链接。

问题如下：

I defined two classes:

class A { def method1 = this }
class B extends A { def method2 = this }

val b = new B

Then I checked the type of b.method1:

scala> b.method1.getClass
res29: Class[_ <: A] = class B

In this case, I cannot use b.method1.method2:

scala> b.method1.method2
<console>:11: error: value method2 is not a member of A
              b.method1.method2

So I have to define A and B like this:

class A { def method1: this.type = this } 
class B extends A { def method2: this.type = this } 

val b = new B

Now I check the type of b.method1:

scala> b.method1.getClass
res31: Class[_ <: B] = class B

Here b.method1.method2 works:

scala> b.method1.method2
res32: b.type = B@4ff3ac

My question here is what does it mean by saying Class[_ <: A] = class B and Class[_ <: B] = class B? And why does the first doesn't work as Class[_ <: A] = class B seems to say that it's also class B?

Reactormonk很好地解答了我的疑问：

Let's split the expression Class[_ <: A] = class B. The first part, Class[_ <: A] tells you what the compiler knows at compile time, that b.method1 returns something of type Class[_ <: A]. The second part, class B mentions that you have a class B as value, but the compiler doesn't know that. That's runtime information.

this.type specializes the method for subclasses, where the type inferred from a plain thisdoesn't.

Scala

Here are my own slides of learning Scala: link1 (Chinese), link2 (English).

This link is a Chinese tutorial of Scala.

See "A Tour of Scala" for more information.

Here are two video tutorials of Scala: link1, link2.