第4课：Scala模式匹配、类型系统彻底精通与Spar(3)

Scala模式匹配Scala类型系统Spark源码阅读

2）自定义提取器；下面的例子显示电子邮件地址的提取器对象：

object Test {

def main(args: Array[String]) {

println ("Apply method : " + apply("Zara", ""));

println ("Unapply method : " + unapply("Zara@"));

println ("Unapply method : " + unapply("Zara Ali"));

}

// The injection method (optional)

def apply(user: String, domain: String) = {

user +"@"+ domain

}

// The extraction method (mandatory)

def unapply(str: String): Option[(String, String)] = {

val parts = str split "@"

if (parts.length == 2){

Some(parts(0), parts(1))

}else{

None

}

}

}

六：变量声明中的模式

val (x, y) = (1, 2)

val (q, r) = BigInt(10) /% 3 // 返回商和余数的对偶

val Array(first, second, _*) = arr // 将第一和第二个分别给first和second

七：for表达式中的模式

import scala.collection.JavaConversions.propertiesAsScalaMap

for ((k, v) <- System.getProperties()) // 这里使用了模式

println(k + " -> " + v)

for ((k, "") <- System.getProperties()) // 失败的匹配会被忽略，所以只打印出值为空的键

println(k)

八：样例类

abstract class Amount

// 继承了普通类的两个样例类

case class Dollar(value: Double) extends Amount

case class Currency(value: Double, unit: String) extends Amount

// 样例对象

case object Nothing extends Amount

amt match {

case Dollar(v) => "$" + v