周海汉 2015.5.28
1.概述
scala是基于JVM的，纯面向对象的函数式编程语言。其亮点有采用Actor模式的高并发编程，Java库的无缝采用，函数式编程，静态类型语言。
著名的Play框架即采用scala语言，并且提供scala和java两种编程接口。
学习scala语言，如果有其他语言基础，其独特的地方有如下几点：
第一是 Actor；第二是函数风格；第三case class ；第四是Mixin trait；第五是 XML；第六是单例和伴生对象。
官网：
下载：
http://www.scala-lang.org/download/all.html
http://www.scala-lang.org/download/2.12.0-M1.html
scala ide,基于eclipse
相关网站：
http://www.typesafe.com/get-started
环境准备：
Java 1.6以上
类Unix系统环境和Windows
将其bin目录添加到PATH中。
scala包含
-
scala Scala interactive interpreter 交互解释器
-
scalac Scala compiler 编译器
-
fsc Scala resident compiler
-
scaladoc Scala API documentation generator
-
scalap Scala classfile decoder
执行以上命令分别完成相应功能。
2. 交互命令行
zhh@scala-2.12.0-M1 % scala
Welcome to Scala version 2.12.0-M1 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_45).
Type in expressions to have them evaluated.
Type :help for more information.
scala> help
<console>:8: error: not found: value help
help
^
scala> :help
All commands can be abbreviated, e.g., :he instead of :help.
:edit <id>|<line> edit history
:help [command] print this summary or command-specific help
:history [num] show the history (optional num is commands to show)
:h? <string> search the history
:imports [name name ...] show import history, identifying sources of names
:implicits [-v] show the implicits in scope
:javap <path|class> disassemble a file or class name
:line <id>|<line> place line(s) at the end of history
:load <path> interpret lines in a file
:paste [-raw] [path] enter paste mode or paste a file
:power enable power user mode
:quit exit the interpreter
:replay [options] reset the repl and replay all previous commands
:require <path> add a jar to the classpath
:reset [options] reset the repl to its initial state, forgetting all session entries
:save <path> save replayable session to a file
:sh <command line> run a shell command (result is implicitly => List[String])
:settings <options> update compiler options, if possible; see reset
:silent disable/enable automatic printing of results
:type [-v] <expr> display the type of an expression without evaluating it
:kind [-v] <expr> display the kind of expression's type
:warnings show the suppressed warnings from the most recent line which had any
scala> 3+2
res1: Int = 5
scala> print("hello world")
hello world
3. hello world
zhh@test % vi hello.scala
zhh@test % scalac hello.scala
zhh@test % ls
HelloWorld$.class HelloWorld.class hello.scala
zhh@test % scala HelloWorld
No such file or class on classpath: HelloWorld
zhh@test % scala -classpath . HelloWorld
Hello, world!
zhh@test % cat hello.scala
object HelloWorld {
def main(args: Array[String]) {
println("Hello, world!")
}
}
object关键字相当于java语言的static，是scala语言的单例模式。scala语言的类型放在变量的后面，用冒号：隔开。这和go语言，swift语言类似。
用scalac进行编译，用scala执行。参数-classpath . 表示指定当前目录为classpath。
4. 引入Java类
zhh@test %
zhh@test % scalac javaChinaDate.scala
zhh@test % scala -classpath . ChinaDate
2015年5月28日
zhh@test % cat javaChinaDate.scala
import java.util.{Date, Locale}; import java.text.DateFormat; import java.text.DateFormat._
object ChinaDate {
def main(args: Array[String]) {
val now = new Date
val df = getDateInstance(LONG, Locale.CHINA); println(df format now)
}
}
引入java类。其中
java.util.{Date, Locale}
是scala语法糖。scala语法可以有分号，也可以省。但两个语句写在一行时分号则不能省。
5. 回调函数实现timer
zhh@test % vi timer.scala
object Timer {
def oncePerSecond(callback: () => Unit) {
while (true) { callback(); Thread sleep 1000 } }
def timeFlies() {
println("time flies like an arrow...")
}
def main(args: Array[String]) {
oncePerSecond(timeFlies)
}
}
一秒打印一句话。其中()=>Unit 表示一个无参函数，返回类型为Unit。Unit在scala语言中相当于c语言的void。
zhh@test % scalac timer.scala
zhh@test % scala -classpath . Timer
time flies like an arrow…
time flies like an arrow…
6.匿名回调函数实现Timer
zhh@test % vi timeranony.scala
zhh@test % scalac timeranony.scala
zhh@test % scala -classpath . TimerAnonymous
time flies like an arrow…
abloz.com
time flies like an arrow…
abloz.com
time flies like an arrow…
abloz.com
^C
zhh@test % cat timeranony.scala
object TimerAnonymous {
def oncePerSecond(callback: () => Unit) {
while (true) { callback(); Thread sleep 1000 }
}
def main(args: Array[String]) {
oncePerSecond(() =>{
println("time flies like an arrow...");
println("abloz.com")
}
) }
}
=>后面直接跟函数体，没有指定回调函数名字，直接用()=>{…}代替定义的回调函数timeFlies。
如非注明转载, 均为原创. 本站遵循知识共享CC协议,转载请注明来源
