learning scala Option[T]

Option(选项)类型用来表示一个值是可选的(有值或无值). Option[T] 是一个类型为 T 的可选值的容器: 如果值存在, Option[T] 就是一个 Some[T] ,如果不存在, Option[T] 就是对象 None val myMap: Map[String, String] = Map("key1" -> "value") val value1: Option[String] = myMap.get("key1") v…

scala Option 里的 orNull orElse getOrElse 区别和使用

Scala Option Scala Option类型用来表示一个值是可选的(有值或无值) Option[T] 是一个类型为 T 的可选值的容器: 如果值存在, Option[T] 就是一个 Some[T] 如果不存在, Option[T] 就是对象 None Option.orNull 参数:没有(当属性用) 返回:如果Option不为None返回Some的值否则返回null 例一:返回Some的值 scala> val v = Some("Hello Option") v:…

Scala Option 从官方DOC解析

Represents optional values. Instances of Option are either an instance of scala.Some or the object None.Option类代表可选的值.Option的实例要么是Some的实例,要么是None的实例. The most idiomatic way to use an scala.Option instance is to treat it as a collection or monad and u…

Scala Option类型

转载自: Scala 初学者指南, 这里有一系列很棒的文章类型 Option 可能你已经见过它在 Map API 中的使用:在实现自己的提取器时,我们也用过它, 然而,它还需要更多的解释. 你可能会想知道它到底解决什么问题,为什么用它来处理缺失值要比其他方法好, 而且可能你还不知道该怎么在你的代码中使用它. 这一章的目的就是消除这些问号,并教授你作为一个新手所应该了解的 Option 知识. Scala 语言中包含一个标准类型 Option[A] 类型, Option[A] 是一个类型为 A…

learning scala Function Recursive Tail Call

可以使用scala库,可以从字面上看出是在调用递归函数: code import scala.util.control.TailCalls._ val arrayDonuts: Array[String] = Array("Vanilla Donut", "Strawberry Donut", "Plain Donut", "Glazed Donut") println("\nStep : How to defin…

learning scala extractor object

package com.aura.scala.day01 import scala.util.Random object extractorObject { def main(args: Array[String]): Unit = { // val customer1ID = CustomerID("Sukyoung") // Sukyoung--23098234908 // customer1ID match { // case CustomerID(name) => pri…

learning scala 数组和容器

数组:可变的,可索引的,元素具有相同类型的数据集合一维数组 scala> val intValueArr = new Array[Int](3)intValueArr: Array[Int] = Array(0, 0, 0) scala> val myStrArr = Array("BigData","hadoop","spark")myStrArr: Array[String] = Array(BigData, hadoop, s…

learning scala control statement

1 .if satement 与其它语言不同的是,scala if statement 返回的是一个值 scala> val a = if ( 6 > 0 ) 1 else -1a: Int = 1 2. while statement 3. do.. while statement 4 for statement for ( 变量 <- 表达式 ) { 语句块}: scala> for ( i <- 1 to 3 ) println(i)123 scala> for…

learning scala read from file

scala读文件: example: scala> import scala.io.Sourceimport scala.io.Source scala> var inputFile = Source.fromFile("text.txt")inputFile: scala.io.BufferedSource = non-empty iterator scala> for ( line <- inputFile.getLines()) println(lin…

learning scala write to file

scala 写文件功能: scala> import java.io.PrintWriterimport java.io.PrintWriter scala> val outputFile = new PrintWriter("text.txt")outputFile: java.io.PrintWriter = java.io.PrintWriter@213c812a scala> outputFile.println("hello panzidong&q…

learning scala output to console

控制台输出语句: print println example: scala> print("i=");print(i)i=345scala> println("hello ");println("world")hello world…

learning scala read from console

控制台输入语句: readInt, readDouble, readByte, readShort, readLong, readChar, readBoolean, readLine example:scala> import io.StdIn._import io.StdIn._ scala> var i=readInt()2i: Int = 2 scala> var f=readFloat()2.2f: Float = 2.2 scala> var b=readBoolean…

learning scala 变量

scala 变量: val : 声明时,必须被初始化,不能再重新赋值. scala> test = "only1"<console>:11: error: not found: value test test = "only1" ^<console>:12: error: not found: value test val $ires0 = test ^ var :可被多次赋值. scala> var test2 = &qu…

learning scala 操作符

scala 操作符: 算术运算符: + - * / % 关系统运算符: > , < ,= ,!= ,>=,<=, 逻辑运算符: && . || , ! 位运算符:&, |, ^,~,<<,>>,>>>(无符号右移) 赋值运算符: = 优先及由上及下…

learning scala akka ask_pattern

package com.example import akka.actor._ import akka.util.Timeout object Tutorial_03_Ask_Pattern extends App { val system = ActorSystem("DonutStoreActorySystem") val donutInfoActor = system.actorOf(Props[DonutInfoActor], name="DonutInfoActor…

learning scala akka actorySystem create and close

package com.example import akka.actor.ActorSystem import scala.util.{Failure, Success} import scala.concurrent.ExecutionContext.Implicits.global object Tutorial_01_ActorSystem_Introduction extends App { println("Step1 : Create an actor system")…

learning scala extracors example

object Twice { def apply(x: Int): Int = x * def unapply(z: Int): Option[Int] = == ) Some(z / ) else None } object TwiceTest extends Application { val x = Twice() x match { case Twice(n) => Console.println(n) } // prints 21 } object TwiceTest extends…

learning scala someElements

The Scala collections library provides specialised implementations for Sets of fewer than 5 values (see the source). The iterators for these implementations return elements in the order in which they were added, rather than the consistent, hash-based…

learning scala implicit class

隐式类可以用来扩展对象的功能非常方便 example: object ImplicitClass_Tutorial extends App { println("Step 1: How to define a case class to represent a Donut object") case class Donut(name: String, price: Double, productCode: Option[Long] = None) println("\nSte…

learning scala PartialFunction

Partial函数的定义 scala> val isVeryTasty: PartialFunction[String, String] = { case "Glazed Donut" | "Strawberry Donut" => "Very Tasty"}isVeryTasty: PartialFunction[String,String] = <function1> scala> isVeryTasty(&qu…

learning scala How To Create Variable Argument Function - varargs :_ *

Scala collection such as List or Sequence or even an Array to variable argument function using the syntax :_ *. code : def printReport(names: String*) { println(s"""Donut Report = ${names.mkString(" - ")}""") } prin…

learning scala generic classes

package com.aura.scala.day01 object genericClasses { def main(args: Array[String]): Unit = { val stack = new Stack[Int] stack.push() stack.push() println(stack.pop()) println(stack.pop()) } } class Stack[A] { private var elements: List[A] = Nil def p…