Scala-Trait:混入与多态

　　Scala 的 Trait 结合了抽象类与接口的能力，通过混入来获得灵活的多态能力。

　　代码如下所示： FileAbility 提供了读取文件、处理文件的能力， 其中继承一个空实现的 Trait：LineHandler， 类似于模板方法模式； 在 ScalaTraitDemo 的 handleFile 方法中，动态定义了两个 Trait , 在新生成的 FileAbility 对象中混入了这两个 Trait 的功能，并且实现了链式处理，类似于装饰器模式。

package scalastudy.basic

/**
* Created by lovesqcc on 16-3-27.
*/
trait LineHandler {
def handle(line: String):Any = {}
}　　

package scalastudy.basic

import scala.io.Source

/**
* Created by lovesqcc on 16-3-27.
*/
trait FileAbility extends LineHandler {

def readFile(filename:String): String = {
val fileSource =  Source.fromFile(filename)
try {
return fileSource.mkString
} finally {
fileSource.close()
}
}

def readFileLines(filename:String):List[String] = {
val fileSource =  Source.fromFile(filename)
try {
return fileSource.getLines().toList
} finally {
fileSource.close()
}
}

def handleFile(filename:String):List[Any] = {
return readFileLines(filename).map(handle(_)).toList
}

def handleFileWithNoReturn(filename:String, lineHandler: LineHandler):Unit = {
readFileLines(filename).foreach { line =>
lineHandler.handle(line)
}
}

}

package scalastudy.basic

import java.util

/**
* Created by lovesqcc on 16-3-19.
*/
object ScalaTraitDemo extends App {

launch()

def launch(): Unit = {
handleFile("/etc/passwd")
}

def handleFile(filename:String):Unit = {

trait LinePrintHandler extends LineHandler {
override def handle(line: String): Any = {
println(line)
}
}

val fileAbility = new FileAbility with LinePrintHandler
fileAbility.handleFile(filename)

trait LineSplitterHandler extends LineHandler {
override def handle(line: String): Any = {
return super.handle(line.split(":").mkString("(", ",", ")"))
}
}

trait LineNumberHandler extends LineHandler {
var id = 0
override def handle(line:String): Any = {
id += 1
//println("number: " + line);
return id + ": " + line
}
}

val fileAbility2 = new FileAbility with LineNumberHandler with LineSplitterHandler
val result = fileAbility2.handleFile(filename)
result.foreach { ref =>
ref match {
case s:String => println(s)
case a:Array[Any] =>  for(e <- ref.asInstanceOf[Array[Any]]) {println(e)}
case a:List[Any] =>  for(e <- ref.asInstanceOf[List[Any]]) {println(e)}
case _ => println(ref)
}
}

}

}