Scala For Java的一些參考

来源:http://www.cnblogs.com/2018/archive/2016/04/08/5366541.html
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變數 String yourPast = "Good Java Programmer"; val yourPast : String = "Good Java Programmer" val yourPast = "Good Java Programmer" var yourFuture = "Go ...


     

變數

String yourPast = "Good Java Programmer";

val yourPast : String = "Good Java Programmer"

val yourPast = "Good Java Programmer"

var yourFuture = "Good Java Programmer"

自動類型推斷；可變、不可變變數

class Money(amount:Int) amount不是成員變數

class Money(val amount:Int)

val notMuch = new Money(2)

notMuch.amount

class Money(var amount:Int)

val notMuch = new Money(2)

notMuch.amount=3

case classes

public class Money {

private Integer amount;

private String currency;

public Money(Integer amount, String currency) {

this.amount = amount;

this.currency = currency;

}

public Integer getAmount() {

return amount;

}

public void setAmount(Integer amount) {

this.amount = amount;

}

public String getCurrency() {

return currency;

}

public void setCurrency(String currency) {

this.currency = currency;

}

@Override

public int hashCode() {

int hash = 5;

hash = 29 * hash + (this.amount != null ? this.amount.

hashCode() : 0);

hash = 29 * hash + (this.currency != null ? this.currency.

hashCode() : 0);

return hash;

}

@Override

public boolean equals(Object obj) {

if (obj == null) {

return false;

}

if (getClass() != obj.getClass()) {

return false;

}

final Money other = (Money) obj;

return true;

}

@Override

public String toString() {

return "Money{" + "amount=" + amount + ", currency=" +

currency + '}';

}

public Money add(Money other) {

return new Money(this.amount +

other.amount, this.currency);

}

}

case class Money(amount:Int=1, currency:String="USD")  two immutable fields the fields declared in Scala classes are public

case class Money(private val amount: Int, private val currency: String)

to make them private instead, or used  var instead of  val to make the fields mutable.

val defaultAmount = Money()

val fifteenDollars = Money(15,"USD")

val fifteenDollars = Money(15)

val someEuros = Money(currency="EUR")

case class Money(val amount:Int=1, val currency:String="USD"){

def +(other: Money) : Money = Money(amount + other.amount)

}

Money(12) + Money(34)

collections

Scala collections are, by default, immutable

val numbers = List(1,2,3,4,5,6)

val reversedList = numbers.reverse

val onlyAFew = numbers drop 2 take 3

cons operator

val numbers = 1 :: 2 :: 3 :: 4 :: 5 :: 6 :: Nil

val simpleList = Nil.::(6)

val twoElementsList = List(6).::(5)

列表串接

val concatenatedList = simpleList ::: twoElementsList

val things = List(0,1,true) AnyVal

val things = List(0,1,true,"false") Any

複雜對象列表

val amounts = List(Money(10,"USD"),Money(2,"EUR"),Money(20,"GBP"),

Money(75,"EUR"),Money(100,"USD"),Money(50,"USD"))

Filter

val euros = amounts.filter(money => money.currency=="EUR")

val euros = amounts.filter(x => x.currency=="EUR")

val euros = amounts.filter(_.currency=="EUR")

partition

val allAmounts = amounts.partition(amt => amt.currency=="EUR")

Tuples

val euros = allAmounts._1

val everythingButEuros= allAmounts._2

val (euros,everythingButEuros) = amounts.partition(amt => amt.currency=="EUR")

Map

Map amounts = new HashMap<String,Integer>();

amounts.put("USD", 10);

amounts.put("EUR", 2);

val wallet = Map( "USD" -> 10, "EUR" -> 2 )

val someEuros = wallet("EUR")

Option類型

val mayBeSomePounds = wallet.get("GBP")

val updatedWallet = wallet + ("GBP" -> 20)  新的不可變

val tenDollars = "USD"-> 10 Tuple
   

def increment = (x:Int) => x + 1

List(1,2,3,4).map(increment)

List(1,2,3,4) map increment

String Interpolation

val many = 10000.2345

val amount = s"$many euros"

格式化寬度

val amount = f"$many%12.2f euros"

val amount = s"${many*2} euros"

val printedAmounts = amounts map(m=> s"${m.amount} ${m.currency}")

groupBy

groupBy method that transforms a collection into a  Map collection:

val sortedAmounts = amounts groupBy(_.currency)

Scala UnitTest

POM.xml maven依賴文件

•  Dependency for the core scala-library:

<dependency>

<groupId>org.scala-lang</groupId>

<artifactId>scala-library</artifactId>

<version>2.10.0</version>

</dependency>

•  Dependency for scalatest (a framework for testing in Scala that supports

JUnit and other styles; we will cover it in detail in Chapter 4, Testing Tools):

<dependency>

<groupId>org.scalatest</groupId>

<artifactId>scalatest_2.10</artifactId>

<version>2.0/version>

<scope>test</scope>

</dependency>

•  Dependency for JUnit to use Java  Assert statements in our test case:

<dependency>

<groupId>junit</groupId>

<artifactId>junit</artifactId>

<version>4.11</version>

<scope>test</scope>

</dependency>

scala-maven-plugin

<plugin>

<groupId>net.alchim31.maven</groupId>

<artifactId>scala-maven-plugin</artifactId>

<executions>

<execution>

<id>scala-compile-first</id>

<phase>process-resources</phase>

<goals>

<goal>add-source</goal>

<goal>compile</goal>

</goals>

</execution>

<execution>

<id>scala-test-compile</id>

<phase>process-test-resources</phase>

<goals>

<goal>testCompile</goal>

</goals>

</execution>

</executions>

</plugin>

單元測試代碼

import org.junit._

import Assert._

class CustomerScalaTest {

  @Before

  def setUp: Unit = {

  }

  @After

  def tearDown: Unit = {

  }

  @Test

  def testGetCustomerId = {

    System.out.println("getCustomerId")

    val instance = new Customer()

    val expResult: Integer = null

    val result: Integer = instance.getCustomerId()

    assertEquals(expResult, result)

  }

}

Java/Scala Collection轉換

./activator console

import java.util.Arrays

val javaList = Arrays.asList(1,2,3,4)

import scala.collection.JavaConverters._

val scalaList = javaList.asScala

val javaListAgain = scalaList.asJava

assert( javaList eq javaListAgain)

JavaBean-style properties

class Company(var name:String)

val sun = new Company("Sun Microsystems")

sun.name

sun.name_=("Oracle")

import scala.beans.BeanProperty

class Company(@BeanProperty var name:String)

val sun = new Company("Sun Microsystems")

sun.getName()

sun.setName("Oracle")

OO

class Customer ( var customerId: Int, var zip: String) {

def this( zip: String) = this(0,zip)

def getCustomerId() = customerId

def setCustomerId(cust: Int): Unit = {

customerId = cust

}

}

val customer = new Customer("123 45")

traits

interface VIPCustomer {

Integer discounts();

}

class Customer(val name:String, val discountCode:String="N" ){

def discounts() : List[Int] = List(5)

override def toString() = "Applied discounts: " + discounts.mkString(" ","%, ","% ")

}

trait VIPCustomer extends Customer {

  override def discounts = super.discounts ::: List(10)

}

trait GoldCustomer extends Customer {

override def discounts =

  if (discountCode.equals("H"))

     super.discounts ::: List(20)

  else super.discounts ::: List(15)

}

object Main {

def main(args: Array[String]) {

val myDiscounts = new Customer("Thomas","H") with VIPCustomer with GoldCustomer

println(myDiscounts)

}

}

scala> Main.main(Array.empty)

Applied discounts: 5%, 10%, 20%

Note that the order in which traits are stacked is important. They are calling each other from right to left.  GoldCustomer is, therefore, the first one to be called.

Static

companion objects

object Main {

def main(args: Array[String]) {

println("Hello Scala World !")

}

}

object Customer {

def apply()= new Customer("default name")

}

class Customer(name:String) {

…

}

exceptions

public class ConversionSample {

static Integer parse(String numberAsString) {

Integer number = null;

try {

number = Integer.parseInt(numberAsString);

} catch (NumberFormatExceptionnfe) {

System.err.println("Wrong format for "+numberAsString);

} catch (Exception ex) {

System.err.println("An unknown Error has occurred");

}

System.out.println("Parsed Number: "+number);

return number;

}

def parse(numberAsString: String) =

try {

Integer.parseInt(numberAsString)

} catch {

case nfe: NumberFormatException =>

println("Wrong format for number "+numberAsString)

case e: Exception => println("Error when parsing number"+

numberAsString)

}

返回值

case nfe: NumberFormatException =>

println("Wrong format for number "+numberAsString); -1

case _: Throwable =>

println("Error when parsing number "+numberAsString)

-1

scala.util.Left or  scala.util.Right type

case class Failure(val reason: String)

def parse(numberAsString: String) : Either[Failure,Int] =

try {

val result = Integer.parseInt(numberAsString)

Right(result)

} catch {

case _ : Throwable => Left(Failure("Error when parsing

number"))

}
 

String customerLevel = null;

if(amountBought > 3000) {

customerLevel = "Gold";

} else {

customerLevel = "Silver";

}

val amountBought = 5000

val customerLevel = if (amountBought> 3000) "Gold" else "Silver"

Scala的代碼風格

IDE

  http://docs.scala-lang.org/style/

Eclipse-based (including all the different versions of Eclipse, Typesafe's own bundled version known as Scala IDE as well as more commercial IDEs such as SpringSourceSTS), IntelliJ IDEA, and NetBeans.

SBT

Simple Build Tool (SBT) http://www.scala-sbt.org/

http://www.scala-sbt.org/0.13/tutorial/Hello.html 例子

http://www.scala-sbt.org/0.13/tutorial/Directories.html 目錄結構，Build.sbt是sbt的定義文件

SBT plugins

https://github.com/typesafehub/sbteclipse 基於sbt生成eclipse使用的工程文件

https://github.com/mpeltonen/sbt-idea 基於sbt生成IntelliJ使用的工程文件

https://github.com/dcaoyuan/nbscala/wiki/SbtIntegrationInNetBeans 基於sbt生成Netbeans使用的工程文件

  plugins.sbt中修改以生成

xsbt-web-plugin (available at  https://github.com/JamesEarlDouglas/xsbt-web-plugin ), a useful plugin to create traditional web apps that runs on a servlet container (such as Jetty).

v Plugins.sbt： addSbtPlugin("com.earldouglas" % "xsbt-web-plugin" % "0.4.2")

Build.sbt：

  name := "SampleProject"

organization := "com.samples"

version := "1.0"

scalaVersion := "2.10.3"

seq(webSettings :_*)

libraryDependencies += "org.mortbay.jetty" % "jetty" % "6.1.22" % "container"

libraryDependencies += "javax.servlet" % "servlet-api" % "2.5" % "provided"

v sbt eclipse生成了eclipse工程

v 啟動web工程

> sbt

> container:start

v War包生成 > package

sbt-assembly

https://github.com/sbt/sbt-assembly

v Plugins.sbt addSbtPlugin("com.eed3si9n" % "sbt-assembly" % "0.11.2")

v assembly.sbt

import AssemblyKeys._ // put this at the top of the file

assemblySettings

// your assembly settings here

Scalariform

plugins.sbt

addSbtPlugin("com.typesafe.sbt" % "sbt-scalariform" % "1.2.0")

SBT中運行compile or  test:compile時，即按照scala風格格式化代碼

Scala Worksheets

Eclipse中建立的菜單

wpsA257.tmp

每次保存時，可以看到執行的結果

wpsA258.tmp

Java基礎庫上scala的封裝例子

http://dispatch.databinder.net/Dispatch.html HttpClient上的封裝

build.sbt添加libraryDependencies += "net.databinder.dispatch" %% "dispatch-core" % "0.11.0"

import dispatch._, Defaults._

val request = url("http://freegeoip.net/xml/www.google.com")

val result = Http( request OK as.String)

val resultAsString = result()

def printer = new scala.xml.PrettyPrinter(90, 2)

for (xml <- citiesAsXML)

println(printer.format(xml))

for comprehension or  for expression

for (sequence) yield expression In the preceding code,  sequence can contain the following components:

•  Generators: They drive the iteration and are written in the following form:

element <- collection

•  Filters: They control the iteration and are written in the following form:

if expression

•  Definitions: They are local variable definitions and are written in the

following form:

variable = expression

for {

elem <- List(1,2,3,4,5)

} yield "T" + elem

for {

word <- List("Hello","Scala")

char <- word

} yield char.isLower

for {

word <- List("Hello","Scala")

char <- word if char.isUpper

} yield char

or {

word <- List("Hello","Scala")

char <- word

lowerChar = char.toLower

} yield lowerChar

測試

ScalaTest ( www.scalatest.org ) and Specs2 ( etorreborre.github.io/specs2/ ). ScalaCheck framework ( www.scalacheck.org )

Typesafe Activator包含必要的插件，項目根下執行> activator eclipse即生成eclipse工程

import org.scalatest.FunSuite

class Test01 extends FunSuite {

test("Very Basic") {

assert(1 == 1)

}

test("Another Very Basic") {

assert("Hello World" == "Hello World")

}

}

> activator

> test-only scalatest.Test01 (or scalatest.Test01.scala)

>~test-only scalatest.Test02  文件修改後自動運行單元測試【continuous mode】

The continuous mode works for the other SBT commands as well, such as  ~run or  ~test

作為Junit的單元測試方式運行

import org.junit.runner.RunWith

import org.scalatest.junit.JUnitRunner

import org.scalatest.FunSuite

@RunWith(classOf[JUnitRunner])

class MyTestSuite extends FunSuite ...

www.seleniumhq.org 功能測試

package scalatest

import org.scalatest._

import org.scalatest.selenium.WebBrowser

import org.openqa.selenium.htmlunit.HtmlUnitDriver

import org.openqa.selenium.firefox.FirefoxDriver

import org.openqa.selenium.WebDriver

class Test08 extends FlatSpec with Matchers with WebBrowser {

implicit val webDriver: WebDriver = new HtmlUnitDriver

go to "http://www.amazon.com"

click on "twotabsearchtextbox"

textField("twotabsearchtextbox").value = "Scala"

submit()

pageTitle should be ("Amazon.com: Scala")

pageSource should include("Scala Cookbook: Recipes")

}

www.scalamock.org

Web框架

alternatives to create web applications range from lightweight frameworks such as Unfiltered, Spray, or Scalatra to full-featured solutions such as the Lift or the Play Frameworks.

http://www.playframework.com/ http://www.playmodules.net

wpsA269.tmp

Web Service

Plugins.sbt

addSbtPlugin("com.typesafe.sbteclipse" % "sbteclipse-plugin" %"2.4.0")

addSbtPlugin("org.scalaxb" % "sbt-scalaxb" % "1.1.2")

resolvers += Resolver.sonatypeRepo("public")

build.sbt

import ScalaxbKeys._

name:="wssample"

scalaVersion:="2.10.2"

scalaxbSettings

ibraryDependencies += "net.databinder.dispatch" %% "dispatch-core" %"0.11.0"

libraryDependencies += "org.scalatest" %% "scalatest" % "2.0.M7" %"test"

sourceGenerators in Compile <+= scalaxb in Compile

packageName in scalaxb in Compile := "se.wssample"

XML/JSON

val books =

<Library>

<book title="Programming in Scala" quantity="15" price="30.00"

/>

<book title="Scala for Java Developers" quantity="10"

price="25.50" />

</Library>

import scala.xml._

val sameBooks = XML.loadString("""

<Library>

<book title="Programming in Scala" quantity="15"

price="30.00"/>

<book title="Scala for Java Developers" quantity="10"

price="25.50"/>

</Library>

""")

val total = (for {

book <- books \ "book"

price = ( book \ "@price").text.toDouble

quantity = ( book \ "@quantity").text.toInt

} yield price * quantity).sum

val books =

<Library>

{ List("Programming in Scala,15,30.00","Scala for Java

Developers,10,25.50") map { row => row split "," } map { b => <book

title={b(0)} quantity={b(1)} price={b(2)} /> }}

</Library>

import scala.util.parsing.json._

val result = JSON.parseFull("""

{

"Library": {

"book": [

{

"title": "Scala for Java Developers",

"quantity": 10

},

{

"title": "Programming Scala",

"quantity": 20

}

]}

}

""")

Futures and Promises

Scala Improvement Process (SIP)SIP-14-Futures and Promises

http://en.wikipedia.org/wiki/Futures_and_promises

•  async { <expression> } : In this construct,  <expression> is the code to

be executed asynchronously.

•  await { <expression returning a Future> } : This construct is included

in an  async block. It suspends the execution of the enclosing  async block

until the argument  Future is completed.

async future

Actor

Reactive Systems

http://www.reactivemanifesto.org/

反應式編程

Misc

MongoDB database, we are going to discover how the Casbah Scala toolkit https://github.com/mongodb/casbah
 

RPEL模式下拷貝部分代碼運行

scala> :paste

// Entering paste mode (ctrl-D to finish)
     

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