This document discusses various Scala concepts and examples: 1. It shows examples of calculating the mean of input numbers, reading lines from a file and splitting into words, and counting word frequencies by building a mutable map. 2. Option, Either, Try, and pattern matching are explained for handling potential failures from operations that return optional values. Collections like Seq, Set, Map are also demonstrated. 3. Examples of integrating Scala and Java are provided like reading/writing files and formatting dates using Java classes.

1. 2019/12/23
Scala Hands On!!

2. 1996
WingArc1st MotionBoard

3. 1.
2.
3.
4.
5. Java
6. ( 1 2)
7. ( 1 2 )

4. 1
val add = calc(2,4,(a,b) => a+b)
val sub = calc(2,4,(a,b) => a-b)
val mul = calc(2,4,(a,b) => a*b)
•
def calc(a: Int, b: Int, f: (Int,Int) => Int ):Int = f(a,b)
f:(Int,Int) Int

5. 1
def addFunc(a: Int, b: Int) = a+b
val add = calc(2,4,addFunc)
•
def calc(a: Int, b: Int, f: (Int,Int) => Int ):Int = f(a,b)
f:(Int,Int) Int

6. 1 0 0 1 0 1 0 0 1 1 1
val list = Seq(9,-4,-2,6,-2,5,0,-7,5,3,10)
list.map(e => if(e>0) 1 else 0).foreach(e => print(e+" "))
1 0 map
1

7. 2
val str = Random.nextInt(10) match {
case 0 | 1 => "0 1"
case i if(i%2 == 0) => " "
case i if(i%3 == 0) => "3 "
case _ => " "
}
• |
• case _

8. 2
•
• case Nil
• l: List[Int]
val list = Seq(1,2,3)
val str1 = list match {
case List(1,a,b) => s"1 and a+b=${a+b}"
case List(x,y) => x+y
case Nil => " "
case l: List[Int] => " :"+l.toString()
case _ => " "
}

9. 3
Option[A] Option[A] Some[A] None
Option
val a: String = null
val option: Option[String] = Option(a)
if(option.isDefined){
println(option.get)
}else{
println("Nothing!!")
}

10. 3
option match {
case Some(x) => f(x)
case None => ()
}
option match {
case Some(x) => Some(f(x))
case None => None
}
option match {
case Some(x) if p(x) => Some(x)
case _ => None
}
option.foreach(println)
option.map(_+"¥n")
option.filter(!_.equals(""))
Option

11. 3
Either
def fileSize(file: File): Either[String,Long] = {
if(file.exists) Right(file.length) else Left("Not exists!!")
}
val f = new File("a/b.txt")
val size: Either[String,Long] = fileSize(f)
if(size.isRight){
println("file size :"+size.right.get)
}else{
println("error :"+size.left.get)
}
Either[A,B] Left[A] Right[B]

12. 3
fileSize(f) match {
case Right(size) => println("file size :"+size)
case Left(str) => println("error :"+str)
}
Either
Left Right

13. 3
Try Option/Either
def div(x: Int,y: Int):Try[Int] = Try(x/y)
div(14,0) match {
case Success(value) => println(value)
case Failure(exception) => exception.printStackTrace()
}
Try(x/y) Failure[Trowable]
Success(x/y)
java.lang.ArithmeticException Failure

14. 4
scala.collection.immutable scala.collection.mutable
immutable

15. 4
Seq C A B...C … A
B
A
DC A
key value
B
C
1
3
2Set Map

16. 4
Seq //
val seq = Seq("A","B","C","B","G")
//
val b = seq(1) //
val head = seq.head //
val last = seq.last //
//
val newSeq1 = seq :+ "F" //
val newSeq2 = seq +: "F" //
val newSeq3 = seq ++ Seq("1","2","3")

17. 4
//
val set = Set("A","B","C","B","G")
//
val contains:Boolean = set("C")
//
val newSet1 = set + "F"
val newSet2 = set ++ Set("F","G","5")
Set

18. 4
Map //
val map = Map("Apple" -> 140, "Orange" -> 90)
// key value
val apple = map("Apple")
val lemon = map.get(“Lemon”) // Option
//
val newMap1 = map + ("Banana"->110)
val newMap2 = map ++ Map("Banana"->110,"Lemon"->70)

19. 4
• flatten
•
val words = Iterable(
Seq("H","e","l","l","o"),
Seq(" ","S","c","a","l","a"),
Seq("!","!"))
println(words.flatten)
List(H, e, l, l, o, , S, c, a, l, a, !, !)
Hello!!
val s = Seq("H","e","l","l","o","!","!")
val hello = s.foldLeft("")((accumurator,element) =>
accumurator + element
)
println(hello)

20. 4

21. 5 Java
import java.util.{Date, Locale}
import java.text.DateFormat._
val now = new Date
val df = getDateInstance(LONG,Locale.ENGLISH)
println(df.format(now))
Java
•
• _ Java *

22. 5 Java
val file:Path = Paths.get("file.txt")
val lines:List[String] = Files.readAllLines(file)
lines.asScala.foreach(println)
import java.nio.file.Path
import java.nio.file.Paths
import java.nio.file.Files
import java.util.List
import scala.collection.JavaConverters._
.asScala .asJava
Java
Scala

23. 6
( )
input: 10 ss 20
mean: 15.0
input: ewqg 3 4 f500 3 5 8 4 5 6 0 w 5
mean: 4.3
1

24. 6
• ( )
val in:Array[String] = StdIn.readLine().split(" ")
val str:String = "14"
val i:Int = str.toInt
• String Int
java.lang.NumberFormatException
•
val list = Iterable(10,44,23,47)
val size: Int = list.size

25. 6
2

26. 6

27. 7
1 2

28. 1
import scala.io.StdIn
import scala.util.Try
import scala.util.Success
import scala.util.Failure

29. 1
def parseInt(str: String): Option[Int] = {
Try(str.toInt) match {
case Success(value) => Some(value)
case Failure(exception) => None
}
}
def inputNums():Iterable[Int]= {
val in:Array[String] = StdIn.readLine().split(" ")
val nums = in
.map(parseInt(_)) // Option
.filter(_.isDefined) // None
.map(_.get) //
nums
}
Int

30. 1
def mean(sample: Iterable[Int]): Double = {
val sum = sample.foldLeft(0)((a,b)=>a+b) //
sum/sample.size.toDouble //
}
print("input: ")
val sample = inputNums()
val res = mean(sample)
println(" mean: "+res)
main

31. 2
import scala.io.Source
import scala.util.Try
import scala.util.Success
import scala.util.Failure
import scala.collection.mutable

32. 2
def getLinesFromfile(path: String):Iterable[String] = {
Try(Source.fromFile(path,"UTF-8")) match {
case Success(value) => value.getLines().toIterable
case Failure(e) => e.printStackTrace();Nil
}
}
I hava a dream.
I have a dream today. I hava a dream. I hava a dream today.

33. 2
1 1
def toWords(lines: Iterable[String]): Iterable[String] = {
val remove = (ward: String,keys: Set[Char]) => ward.filter(!keys(_))
lines.map(_.split(" ")).flatten
.map(remove(_,Set('¥n','.',',','“','”','¥'','’','–')))
}
I hava a dream. I hava a dream today.
I have a dream I have a dream today

34. 2
main
val path = "a/texts/ihaveadream.txt"
//
val wards: Iterable[String] = toWords(getLinesFromfile(path))
//
val set: Set[String] = wards.toSet
//
val keyMap: mutable.Map[String,Int] = mutable.Map.empty ++ set.map(_ -> 0).toMap
//
wards.foreach(keyMap(_)+=1)
//
keyMap.toSeq.sortBy(_._2).foreach(println)
mutable.Map …