Functional and OOP Programming in Scala

// Single line comment

/*
Multiline Comment

*/

/**
  * Documentation comment.
  *
  */

/** This function computes the distance from origin (0, 0) to point (x, y)
  *
  *  Usage Example:
  *
  *  {{{
  *     scala> distancePoint(30.0, 40.0)
  *     res11: Double = 50.0
  *  }}}
  *
  *  @param x  - X coordinate of point
  *  @param y  - Y coordinate of point
  *  @return  Distance from origin to point (x, y)
  */
def distancePoint(x: Double, y: Double) =
  Math.sqrt(x * x + y * y)

scala> val x = 10.2323
x: Double = 10.2323

scala> x = 1.5354
<console>:12: error: reassignment to val
       x = 1.5354

scala> val a = "hello world"
a: String = hello world

  // Scala has multi-line string, unlike Java.
  val s = """Hello world
  Scala
  String
  """

scala> val frame = new javax.swing.JFrame("Hello world")
frame: javax.swing.JFrame = javax.swing.JFrame[frame0,0,27,0x0,invalid,hidden ...]

// --- Try to change the reference stored in the value.
//
scala> val frame2 = new javax.swing.JFrame("Hello world")
frame2: javax.swing.JFrame = javax.swing.JFrame[frame1,0,27 ...]

scala> frame = frame2
<console>:13: error: reassignment to val
       frame = frame2

// A copy of the object previously defined is not created,
// only the reference (pointer) of this object is copied.
//
scala> val frameCopy = frame
frameCopy: javax.swing.JFrame = javax.swing.JFrame[frame3,0,2 ... ..

scala> frame.getTitle
res18: String = Hello world

scala> frameCopy.getTitle
res12: String = Hello world

scala> frame.setTitle("Scalability and growth")

scala> frameCopy.setTitle("Scalability and growth")

scala> frame.getTitle
res22: String = Scalability and growth

scala> frame.setTitle("Scalable scalable scalable ...")

scala> frameCopy.getTitle
res24: String = Scalable scalable scalable ...

// Eq - Method checks for reference equality. So, if the references (pointer to object) to
// objects are equal, then the return value should be true.
//
scala> frameCopy eq frame
res15: Boolean = true

scala> frameCopy.eq(frame)
res16: Boolean = true

scala> frame.eq(frameCopy)
res17: Boolean = true

scala> val x: Double = 20.03
x: Double = 20.03

scala> val y: Double = "hello world"
<console>:11: error: type mismatch;
 found   : String("hello world")
 required: Double
       val y: Double = "hello world"
                       ^

scala> val point: (Int, Int) = (100, 200)
point: (Int, Int) = (100,200)

scala> val point2: (Int, Int) = -100.34
<console>:11: error: type mismatch;
 found   : Double(-100.34)
 required: (Int, Int)
       val point2: (Int, Int) = -100.34


scala> type Action = () => Unit
defined type alias Action

scala> val act1: Action = () => println("Print to screen1")
act1: Action = $$Lambda$1109/363103401@b56c222

scala> printer1("hello world Scala is super scalable!!")
hello world Scala is super scalable!!

scala> var x = 10.2334
x: Double = 10.2334

scala> x = 4.5
x: Double = 4.5

scala> var s = "Hello"
s: String = Hello

scala> s = "world"
s: String = world

scala>

scala> var x: Double = 10.0
x: Double = 10.0

scala> x = 2
x: Double = 2.0

scala> x = 45.43
x: Double = 45.43


// Declare a variable holding a reference to a function
// with default NULL value.
// WARNING. Null should be used with caution.
scala> var action: String => Unit = null
action: String => Unit = null

scala> action("testing Scala")
java.lang.NullPointerException
  ... 28 elided

scala> action = s => println("Message = " + s)
action: String => Unit = $$Lambda$1171/1365490452@2865c8db

scala> action("testing Scala")
Message = testing Scala

// Print to stderr - Store reference to method (.println) of System.err object.
scala> action = System.err.println
action: String => Unit = $$Lambda$1172/1358395794@2f533bd1

scala> action("testing Scala")
testing Scala

val x = 10 
val y = 15 
val z = x + y 

scala> val x = 10 
x: Int = 10

scala> val y = 15 
y: Int = 15

scala> val z = x + y 
z: Int = 25

// Local Scope 
scala> { val x  = 5 ; val y = 4 ; val z = x + y ; println("z = " + z) }
z = 9

// Values from local scope are not affected by the values of local one.
scala> x
res4: Int = 10

scala> y
res5: Int = 15


scala> val k1 = { println("k1 set to 5.0") ; 5.0 }
k1 set to 5.0
k1: Double = 5.0

scala> 2 * k1
res1: Double = 10.0

val z2 = {
  val a = 2
  val b = 5
  // Return value from scope is the last value
  a + b
}

scala> val z2 = {
     |   val a = 2
     |   val b = 5
     |   // Return value from scope is the last value
     |   a + b
     | }
z2: Int = 7

scala> a
<console>:12: error: not found: value a
       a
       ^

scala> b
<console>:12: error: not found: value b
       b
       ^

scala> import java.io._
import java.io._

scala> val fd = new FileWriter("/tmp/testfile.txt")
fd: java.io.FileWriter = java.io.FileWriter@1eceaded

scala> fd.write("hello world")

scala> fd.close()

scala> import javax.swing.JFrame
import javax.swing.JFrame

scala> import javax.swing.{JFrame, JPanel, JLabel}
import javax.swing.{JFrame, JPanel, JLabel}

scala> val frame = new JFrame("Hello world Scala")

scala> frame.setSize(300, 400)

scala> frame.setVisible(true)

scala> val frame = new javax.swing.JFrame("Hello world Scala")

scala> frame.setSize(300, 400)

scala> frame.setVisible(true)

@ import Math.{PI, sin, cos, tan, exp} 
import Math.{PI, sin, cos, tan, exp}

@ Math.sin(Math.PI) 
res7: Double = 1.2246467991473532E-16

@ sin(PI) 
res4: Double = 1.2246467991473532E-16

@ cos(PI) 
res5: Double = -1.0

@ exp(-2.0) 
res6: Double = 0.1353352832366127

scala> import Math._ // Import everything 
import Math._

// Or: Import all static methods of class java.lang.Math to use them as functions.
scala> import java.lang.Math._
import java.lang.Math._

scala> sin _
res7: Double => Double = $$Lambda$1197/1482753855@56352274

scala> cos _
res8: Double => Double = $$Lambda$1198/1338109470@64deb236

scala> sin(PI)
res9: Double = 1.2246467991473532E-16

scala> List(30, 45, 60, 90, 180).map{x => sin(x * PI / 180.0)} foreach println
0.49999999999999994
0.7071067811865475
0.8660254037844386
1.0
1.2246467991473532E-16

@ object Module{ 
    def fn(x: Int) = x * 3
    def fxy(a: Int, b: Int) = a + b 
    val gravity = 9.81 
  } 
defined object Module

@ Module.fn(4) 
res9: Int = 12

@ Module.fxy(10, 12) 
res10: Int = 22

@ import Module.{fn, fxy} 
import Module.{fn, fxy}

@ fn(4) 
res12: Int = 12

@ fxy(10, 12) 
res13: Int = 22

scala> Math.log10(1000)
res16: Double = 3.0

scala> Math log10 1000
res17: Double = 3.0

scala> List(1.0, 10.0, 100.0, 1000.0, 10000.0).map(Math.log10)
res20: List[Double] = List(0.0, 1.0, 2.0, 3.0, 4.0)

scala> List(1.0, 10.0, 100.0, 1000.0, 10000.0) map Math.log10
res21: List[Double] = List(0.0, 1.0, 2.0, 3.0, 4.0)

def prod(x: Int, y: Int) = x * y

scala> prod(4, 5)
res11: Int = 20


def fun(a: Int, b: Int) = {
  val c = 3 * a + b
  val d = b - a
  c * d // The return value is the last value
}

/**
   a = 4 and b = 5
   c = 3 * a + b = 3 * 4 + 5 = 17
   d = b - a     = 5 - 4 = 1

Return value:
   c * d = 17 * 1

--------------- */
scala> fun(4, 5)
res8: Int = 17


def showFiles(path: String) = {
  val file = new java.io.File(path)
  file.listFiles.foreach(println)
}

// Pasting in the REPL
scala> def showFiles(path: String) = {
     |   val file = new java.io.File(path)
     |   file.listFiles.foreach(println)
     | }
showFiles: (path: String)Unit


scala> showFiles("/")
/home
/var
/bin
/usr
/root
/Applications
/proc
/boot
/dev
... ...

scala> val mulBy10 = (x: Int) => x * 10
mulBy10: Int => Int = <function1>

scala> mulBy10(5)
res25: Int = 50

scala>

scala> val add = (x: Double, y: Double) => x + y
addV1: (Double, Double) => Double = <function2>

scala> add(10, 20)
res26: Double = 30.0

val func = (a: Double, b: Double) => {
  val m = a * b
  val n = a * a * 3 - 4.5 * b
  (m, n, m + n)
}

scala> val func = (a: Double, b: Double) => {
     |   val m = a * b
     |   val n = a * a * 3 - 4.5 * b
     |   (m, n, m + n)
     | }
func: (Double, Double) => (Double, Double, Double) = <function2>

scala> func(3, 5)
res28: (Double, Double, Double) = (15.0,4.5,19.5)

scala> func(4, 3)
res29: (Double, Double, Double) = (12.0,34.5,46.5)

scala>

scala> def mulxy (x: Int, y: Int) = x * y
mulxy: (x: Int, y: Int)Int

scala> mulxy(3, 4)
res37: Int = 12


scala> List(1, 2, 3, 4, 5).map(mulxy(3, _))
res38: List[Int] = List(3, 6, 9, 12, 15)


scala> List(1, 2, 3, 4, 5).map(mulxy(_, 4))
res39: List[Int] = List(4, 8, 12, 16, 20)

scala> def mulxy (x: Int) (y: Int) = x * y
mulxy: (x: Int)(y: Int)Int

scala> mulxy _
res89: Int => (Int => Int) = <function1>

scala> mulxy(3)_
res88: Int => Int = <function1>

scala> mulxy(3)(4)
res90: Int = 12

scala> List(2, 3, 4, 5).map(mulxy(5))
res91: List[Int] = List(10, 15, 20, 25)

scala> List(2, 3, 4, 5) map mulxy(5)
res38: List[Int] = List(10, 15, 20, 25)

scala> val mulNonCurried = (x: Int, y: Int) => x * y
mulNonCurried: (Int, Int) => Int = <function2>

scala> mulNonCurried(3, 5)
res30: Int = 15


scala> val mulCurried = (x: Int) => (y: Int) => x * y
mulCurried: Int => (Int => Int) = <function1>

scala> mulCurried(5)
res32: Int => Int = <function1>

scala> mulCurried(5)(4)
res33: Int = 20

scala> List(1, 2, 3, 4, 5).map(mulCurried(4))
res34: List[Int] = List(4, 8, 12, 16, 20)

scala> List(1, 2, 3, 4, 5)  map mulCurried(4)
res35: List[Int] = List(4, 8, 12, 16, 20)

/**  Pretty print a collection of tuples as a table. 
  Parameters: 
  @rows     - Collection of tuples to be printed.  
  @title    - Tuple containing the titles of left and right side. 
  @line     - Flag that if set to true, prints a new line between each row.
  @margin   - Margin from left side of screen as number of spaces.
  @sep      - Number of spaces between left side and right side 
  @maxRside - Maximum number of characters to printed on right side.
  */ 
def printTupleAsTable(
  rows:   Seq[(String, String)],
  title:  (String, String) = ("", ""),
  line:   Boolean = false,
  margin: Int = 0,
  sep:    Int = 4,
  maxRside: Int = 100
) = {

  def printRow(wmax1: Int, clamp: Boolean = true) = (row: (String, String)) => {
    val (lside, rside) = row

    // print left margin 
    for (a <- 0 to margin) print(' ')

    print(lside)

    // Print spaces 
    for (a <- 0 to wmax1 - lside.length + sep) print(' ')

    if (rside.length <= maxRside) {
      println(rside)
    } else if (clamp){
      val dots = "..."
      println(rside.take(maxRside - dots.length) + dots)
    } else {
      println(rside.take(maxRside))
    }

    // Print line between rows 
    if (line) println()
  }

  def printDashes(wmax1: Int) = {
    printRow(wmax1, false)("-" * wmax1, "-" * maxRside)
  }

  val (title1, title2) = title

  // Maximum length of left side column 
  val wmax1 = title1.length max rows.map(row => row._1.length).max

  printRow(wmax1)(title)
  printDashes(wmax1)
  rows foreach printRow(wmax1)
  printDashes(wmax1)
}

import scala.collection.JavaConverters._

scala> System.getProperties.asScala.toSeq foreach println
(env.emacs,)
(java.runtime.name,OpenJDK Runtime Environment)
(sun.boot.library.path,/usr/lib/jvm/java-8-openjdk/jre/lib/amd64)
(java.vm.version,25.141-b15)
(java.vm.vendor,Oracle Corporation)
(java.vendor.url,http://java.oracle.com/)
(path.separator,:)
(java.vm.name,OpenJDK 64-Bit Server VM)
(file.encoding.pkg,sun.io)
(user.country,US)
(sun.java.launcher,SUN_STANDARD)
... ... ... ... ... ... ... ... ... ... ... ... ... ... 


scala> printTupleAsTable(System.getProperties.asScala.toSeq, title = ("Java Property", "Value"), maxRside = 60)
 Java Property                     Value
 -----------------------------     ------------------------------------------------------------
 env.emacs                         
 java.runtime.name                 OpenJDK Runtime Environment
 sun.boot.library.path             /usr/lib/jvm/java-8-openjdk/jre/lib/amd64
 java.vm.version                   25.141-b15
 java.vm.vendor                    Oracle Corporation
 java.vendor.url                   http://java.oracle.com/
 path.separator                    :
 java.vm.name                      OpenJDK 64-Bit Server VM
 file.encoding.pkg                 sun.io
 user.country                      US
 sun.java.launcher                 SUN_STANDARD
 sun.os.patch.level                unknown
 java.vm.specification.name        Java Virtual Machine Specification
 user.dir                          /home/archbox/test

... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... .

 java.vm.info                      mixed mode
 java.version                      1.8.0_141
 java.ext.dirs                     /usr/lib/jvm/java-8-openjdk/jre/lib/ext:/usr/java/package...
 sun.boot.class.path               /usr/lib/jvm/java-8-openjdk/jre/lib/resources.jar:/usr/li...
 java.vendor                       Oracle Corporation
 file.separator                    /
 java.vendor.url.bug               http://bugreport.sun.com/bugreport/
 sun.io.unicode.encoding           UnicodeLittle
 sun.cpu.endian                    little
 sun.cpu.isalist                   
 -----------------------------     ------------------------------------------------------------



printTupleAsTable(
  rows = System.getenv.asScala.toSeq,
  title = ("Environment Variables", "Value"),
  margin = 5,
  maxRside = 60
)

scala> printTupleAsTable(
     |   rows = System.getenv.asScala.toSeq,
     |   title = ("Environment Variables", "Value"),
     |   margin = 5,
     |   maxRside = 60
     | )
      Environment Variables        Value
      ------------------------     ------------------------------------------------------------
      PATH                         /usr/local/sbin:/usr/local/bin:/usr/bin:/usr/lib/jvm/defa...
      XAUTHORITY                   /home/archbox/.Xauthority
      LC_MEASUREMENT               pt_BR.UTF-8
      LC_TELEPHONE                 pt_BR.UTF-8
      GDMSESSION                   xfce
      XDG_DATA_DIRS                /usr/local/share:/usr/share
      LC_TIME                      pt_BR.UTF-8
      DBUS_SESSION_BUS_ADDRESS     unix:path=/run/user/1001/bus
      XDG_CURRENT_DESKTOP          XFCE
      MAIL                         /var/spool/mail/archbox
      SSH_AGENT_PID                29199
      MOZ_PLUGIN_PATH              /usr/lib/mozilla/plugins
      COLORTERM                    truecolor
      SESSION_MANAGER              local/ghostpc:@/tmp/.ICE-unix/29194,unix/ghostpc:/tmp/.IC...
      LC_PAPER                     pt_BR.UTF-8
      LOGNAME                      archbox
      PWD                          /home/archbox/test

     ... .... ...   ... .... ...   ... .... ...   ... .... ...   ... .... ...   ... .... ...

      EDITOR                       emacs -Q -nw --no-site -eval "(progn (setq  inhibit-start...
      NLSPATH                      /usr/dt/lib/nls/msg/%L/%N.cat
      QT_QPA_PLATFORMTHEME         qt5ct
      XDG_RUNTIME_DIR              /run/user/1001
      XDG_VTNR                     7
      HOME                         /home/archbox
      ------------------------     ------------------------------------------------------------

scala> val f = (x: Int) => x + 10
f: Int => Int = <function1>

scala> val g = (x: Int) => x * 2
g: Int => Int = <function1>


scala> val comp1 = f.compose(g)
comp1: Int => Int = <function1>


scala> comp1(3)
res70: Int = 16

scala> List(1, 2, 3, 4, 5).map(comp1)
res71: List[Int] = List(12, 14, 16, 18, 20)

scala>


/// It could also be:

scala> val comp11 = f compose g
comp11: Int => Int = <function1>

scala> List(1, 2, 3, 4, 5).map(comp11)
res72: List[Int] = List(12, 14, 16, 18, 20)

scala> val f = (x: Int) => x + 10
f: Int => Int = <function1>

scala> val g = (x: Int) => x * 2
g: Int => Int = <function1>

scala> val f_rcomp_g = f andThen g
f_rcomp_g: Int => Int = <function1>

scala> f_rcomp_g (4)
res76: Int = 28

// Or
scala> f.andThen(g)(4)
res77: Int = 28

def sumFn1(f: Int => Int, g: Int => Int, x: Int) = f(x) + g(x)

scala> def sumFn1(f: Int => Int, g: Int => Int) (x: Int) = f(x) + g(x)
sumFn: (f: Int => Int, g: Int => Int)(x: Int)Int


scala>  sumFn1(x => x * 4, a => a + 5, 4)
res46: Int = 25

scala>  sumFn1(x => x * 4, a => a + 5, 5)
res47: Int = 30

scala>  sumFn1(x => x * x, a => a + 5, 5)
res48: Int = 35


def sumFn2(f: Int => Int, g: Int => Int) = (x: Int) => f(x) + g(x)

scala> f1(3)
res49: Int = 20

scala> f1(5)
res50: Int = 30

scala> val f2 = sumFn2(x => x * x, a => a + a)
f2: Int => Int = <function1>

scala> f2(3)
res51: Int = 15

scala> f2(5)
res52: Int = 35



def iterFiles(fn: String => Unit) = (path: String) => {
  val f = new java.io.File(path)
  f.listFiles().foreach(file => fn(file.toString))
}

scala> iterFiles(println)("/")
/home
/var
/bin
/usr
/root
/Applications
/proc
/boot
/dev
  ...

scala> val showFiles = iterFiles(println)
showFiles: String => Unit = <function1>


scala> showFiles("/etc")
/etc/systemd
/etc/motd
/etc/gemrc
/etc/adobe
/etc/ld.so.cache
/etc/environment
/etc/libreoffice
/etc/rc_keymaps
/etc/sensors3.conf
... ...

scala> var printer: (String) => Unit = s => ()
printer: String => Unit = $$Lambda$1031/1414431049@7fb66650

scala> printer("Test printer")

scala> printer = println
printer: String => Unit = $$Lambda$1060/1256918571@648c5fb3

scala> printer("Test printer")
Test printer

// Print to stdout
scala> printer = System.err.println
printer: String => Unit = $$Lambda$1092/1353172779@54c11750

scala> printer("Test printer")
Test printer

scala> var action: () => Unit = () => ()
action: () => Unit

scala> action()


scala> val printMe = () => println("Print me right now")
printMe: () => Unit

scala> action = printMe
action: () => Unit 

scala> action()
Print me right now

object Utils{
  def showLinuxRootFiles() =
    for(f <- new java.io.File("/").listFiles)
      println(f)
}


scala> action = Utils.showLinuxRootFiles _
action: () => Unit 

scala> action()
/etc
/tmp
/sbin
/sys
/opt
/media
/boot
 ... ... ... ... ... ... ... ...


class ProductInventory{
  private val lst = new java.util.ArrayList[String]

  def addProduct(product: String) = {
    println("Logger -> Added " + product)    
    lst.add(product)
  }

  def showInventory() =
    lst.forEach{ p => println("Product = " + p)}
}



scala> val myShopInventory = new ProductInventory()
myShopInventory: ProductInventory = ProductInventory@5a6dbab7

scala> myShopInventory.addProduct("Orange")
Logger -> Added Orange
res11: Boolean = true

scala> myShopInventory.addProduct("Apple")
Logger -> Added Apple
res12: Boolean = true

scala> myShopInventory.addProduct("Coffee beans")
Logger -> Added Coffee beans
res13: Boolean = true

scala> myShopInventory.showInventory()
Product = Orange
Product = Apple
Product = Coffee beans

scala> action = myShopInventory.showInventory _
action: () => Unit = $$Lambda$1369/801054059@4f4a6252

scala> action()
Product = Orange
Product = Apple
Product = Coffee beans

scala> myShopInventory.addProduct("Strawberry")
Logger -> Added Strawberry
res18: Boolean = true

scala> action()
Product = Orange
Product = Apple
Product = Coffee beans
Product = Strawberry

// Dummy - do anything 
scala> val action0 = () => ()
action0: () => Unit = $$Lambda$1375/1357073725@74ddf6f8

scala> val action1 = () => println("Get product from inventory")
action1: () => Unit = $$Lambda$1373/1589324702@6bfa9cf5

scala> val action2 = () => println("Order more replacement parts from the manufacturer X inc.")
action2: () => Unit = $$Lambda$1374/180387583@1c9eb283

def action3() = 
  println("Check company's balance sheet.")

class CompanyData(name: String){
  def printStatements() = {
    println("Print Balance Sheet of company       = " + name)
    println("Print Cash Flow statement of company = " + name)
  }
}

scala> val company = new CompanyData("XZYZW Solution. Inc.")
company: CompanyData = CompanyData@249318e7

//------ Register functions --------------- //

scala> import scala.collection.mutable.ListBuffer
import scala.collection.mutable.ListBuffer

scala> val actionList = ListBuffer[() => Unit]()
actionList: scala.collection.mutable.ListBuffer[() => Unit] = ListBuffer()

scala> actionList.append(action0)
scala> actionList.append(action1)
scala> actionList.append(action2)

scala> for (act <- actionList) act()
Get product from inventory
Order more replacement parts from the fanufacterer X inc.

actionList.append(action3 _)

scala> for (act <- actionList) act()
Get product from inventory
Order more replacement parts from the fanufacterer X inc.
Check company's balance sheet.

// Register method to be called 
scala> actionList.append(company.printStatements _)

scala> for (act <- actionList) act()
Get product from inventory
Order more replacement parts from the fanufacterer X inc.
Check company's balance sheet.
Print Balance Sheet of company       = XZYZW Solution. Inc.
Print Cash Flow statement of company = XZYZW Solution. Inc.

def varfun(inputs: String*) = {
  println("I got the parameters: ")
  inputs.foreach(println)
}

scala> varfun("Hello", "World", "Scala", "Rocks")
I got the parameters:
Hello
World
Scala
Rocks

scala> val xs = List("hello", "World", "Scala", "Rocks")
xs: List[String] = List(hello, World, Scala, Rocks)

scala> varfun(xs)
<console>:14: error: type mismatch;
 found   : List[String]
 required: String
       varfun(xs)
              ^

scala> varfun(xs : _ *)
I got the parameters: 
hello
World
Scala
Rocks

scala> val xs2  = Vector("Java", "everywhere", "in", "desktop", "servers", "mobile")
xs2: scala.collection.immutable.Vector[String] = Vector(Java, everywhere, in, desktop, servers, mobile)

scala> varfun(xs2 :_ *)
I got the parameters: 
Java
everywhere
in
desktop
servers
mobile

/** Free fall speed v(t) = g * t, g in m/s^2 */
def freeFallSpeed(time: Double, gravity: Double = 9.81) = time * gravity

scala> freeFallSpeed(1.0)
res30: Double = 9.81

scala> freeFallSpeed(2.0)
res31: Double = 19.62

scala> freeFallSpeed(2.0, 10.0)
res32: Double = 20.0

scala> freeFallSpeed(2.0, 20.0)
res33: Double = 40.0

scala> freeFallSpeed(2.0, gravity = 10.0)
res35: Double = 20.0

scala> freeFallSpeed(2.0, gravity = 15.0)
res36: Double = 30.0

cala> :paste
// Entering paste mode (ctrl-D to finish)


object Module {

  val code = "xyzfmnk"

  var amount = 1000 

  def sayHello () = println("Hello world")

  def fn(x: Int, y: Int) = 3 * x + 4 * y

  def showFiles(path: String) = {
    val files = (new java.io.File(path)).listFiles().filter(_.isFile)
    files.foreach(println)    
  }

  def showDirectories(path: String) = {
    val files = (new java.io.File(path)).listFiles().filter(_.isDirectory)
    files.foreach(println)    
  }

}

scala> Module.fn _
res204: (Int, Int) => Int = <function2>

scala> Module.sayHello _
res205: () => Unit = <function0>

scala> Module.showFiles _
res206: String => Unit = <function1>

scala> Module.showFiles("/boot")
/boot/initramfs-3.10-x86_64.img
/boot/vmlinuz-4.9-x86_64
/boot/initramfs-3.10-x86_64-fallback.img
/boot/vmlinuz-3.10-x86_64
/boot/initramfs-4.9-x86_64-fallback.img
/boot/initramfs-4.9-x86_64.img
/boot/intel-ucode.img
/boot/linux310-x86_64.kver
/boot/linux49-x86_64.kver

scala> Module.showDirectories("/boot/grub")
/boot/grub/i386-pc
/boot/grub/locale
/boot/grub/fonts
/boot/grub/themes

scala> Module.sayHello()
Hello world

scala> Module.code 
res219: String = xyzfmnk

scala> Module.code = "hello"
<console>:13: error: reassignment to val
       Module.code = "hello"
                   ^

scala> Module.amount += 300

scala> Module.amount
res223: Int = 1300


scala> Module.amount = 0
Module.amount: Int = 0

scala> Module.getClass()
res224: Class[_ <: Module.type] = class Module$

trait Observer{
  def onChange(): Unit
  def onError():  Unit  
}

class Observer1 extends Observer{
  def onChange() =
    println("I received a change event.")

  def onError() =
    println("I received an error event.")
}

object SingleTonObserver extends Observer{
  def onChange() =
    println("Singleton: I received a change event.")

  def onError() =
    println("Singleton: I received an error event.")
}

scala> obs1.onChange()
I received a change event.

scala> obs1.onError()
I received an error event.

scala> SingleTonObserver.onChange()
Singleton: I received a change event.

scala> SingleTonObserver.onError()
Singleton: I received an error event.

def generateErrorEvent(obs: Observer) =
  obs.onError()

scala> generateErrorEvent(obs1)
I received an error event.

scala> generateErrorEvent(SingleTonObserver)
Singleton: I received an error event.

var i = 0
while (i < 10){
   println ("i = " + i)
   i = i + 1
}

scala> var i = 0
i: Int = 0

scala> while (i < 10){
     |    println ("i = " + i)
     |    i = i + 1
     | }
i = 0
i = 1
i = 2
i = 3
i = 4
i = 5
i = 6
i = 7
i = 8
i = 9

val fr  = new java.io.FileReader("/etc/protocols")
val bfr = new java.io.BufferedReader(fr)
val maxLines = 15
var line = ""
var n = 0 

do{
  line = bfr.readLine()
  println(s"Line $n = " + line)
  n = n + 1
} while(line != null && n < maxLines)

println(s"Number of lines read is equal to $n ")

fr.close()
bfr.close()

scala> do{
     |   line = bfr.readLine()
     |   println(s"Line $n = " + line)
     |   n = n + 1
     | } while(line != null && n < maxLines)
Line 0 = # /etc/protocols:
Line 1 = # $Id: protocols,v 1.12 2016/07/08 12:27 ovasik Exp $
Line 2 = #
Line 3 = # Internet (IP) protocols
Line 4 = #
Line 5 = #  from: @(#)protocols 5.1 (Berkeley) 4/17/89
Line 6 = #
Line 7 = # Updated for NetBSD based on RFC 1340, Assigned Numbers (July 1992).
Line 8 = # Last IANA update included dated 2011-05-03
Line 9 = #
Line 10 = # See also http://www.iana.org/assignments/protocol-numbers
Line 11 = 
Line 12 = ip    0   IP      # internet protocol, pseudo protocol number
Line 13 = hopopt    0   HOPOPT      # hop-by-hop options for ipv6
Line 14 = icmp  1   ICMP        # internet control message protocol

scala> println(s"Number of lines read is equal to $n ")
Number of lines read is equal to 15

scala> for (i <- 1 to 10) println(i)
1
2
3
4
5
6
7
8
9
10

scala> for (i <- 1 to 10) println("i = " + i)
i = 1
i = 2
i = 3
i = 4
i = 5
i = 6
i = 7
i = 8
i = 9
i = 10

scala> for (file <- (new java.io.File("/").listFiles)) println(file)
/home
/var
/bin
/usr
/root
/Applications
/proc
/boot
/dev
/opt
/etc
/mnt
/tmp
/run
/desktopfs-pkgs.txt
/lib
/.manjaro-tools
/srv
/lib64
/rootfs-pkgs.txt
/sys
/sbin
/lost+found

@ val s = "  Hello world scala  "  
s: String = "  Hello world scala  "

@ s.size 
res41: Int = 21
@  
@ s size 
res42: Int = 21
@  
@ s.length 
res43: Int = 21

@ s length 
res44: Int = 21
@

@ "Hello" + " " + "world" + " " + "scala" 
res45: String = "Hello world scala"
@

@ s  
res47: String = "  Hello world scala  "
@ s trim 
res48: String = "Hello world scala"
@ s.trim() 
res49: String = "Hello world scala"
@ s trim  
res50: String = "Hello world scala"
@

@ s.replace("scala", "haskell") 
res46: String = "  Hello world haskell  "
@

@ s.toUpperCase 
res60: String = "  HELLO WORLD SCALA  "

@ s.toLowerCase 
res61: String = "  hello world scala  "
@

@ "hello world".startsWith("hello") 
res65: Boolean = true
@  
@ "hello world" startsWith "hello" 
res66: Boolean = true
@

@ "hello world".endsWith("hello") 
res67: Boolean = false
@  
@ "hello world".endsWith("world") 
res68: Boolean = true
@  
@ "hello world" endsWith "world" 
res69: Boolean = true
@

// Operator (==) is not type-safe: 
//
@ "hello" == "world" 
res51: Boolean = false
@ "hello" == "hello" 
res52: Boolean = true

// This inconsistent operation type checks.
@ "hello" == 100 
res53: Boolean = false
@

scala> List("Oversee", "fixed", "income", "assets").mkString(", ")
res11: String = Oversee, fixed, income, assets

scala> List("Oversee", "fixed", "income", "assets") mkString " "
res12: String = Oversee fixed income assets

scala> Vector("Oversee", "fixed", "income", "assets") mkString " "
res13: String = Oversee fixed income assets

scala> Array("Oversee", "fixed", "income", "assets") mkString ":"
res14: String = Oversee:fixed:income:assets

scala> xs.mkString(", ")
res15: String = 1, 2, 3, 4, 5, 6, 7, 8, 9, 10

scala> xs.mkString("; ")
res16: String = 1; 2; 3; 4; 5; 6; 7; 8; 9; 10

scala> val rootDir = new java.io.File("/").listFiles().mkString("\n => ")
rootDir: String =
/etc
 => /tmp
 => /sbin
 => /sys
 => /opt
 => /media
 => /boot
 => /.local
 => /.autorelabel
 => /home

scala> "true".toBoolean
res27: Boolean = true

scala> "false".toBoolean
res28: Boolean = false

scala> "f".toBoolean
java.lang.IllegalArgumentException: For input string: "f"
  at scala.collection.immutable.StringLike.parseBoolean(StringLike.scala:324)

scala> "-128".toByte
res37: Byte = -128

scala> "127".toByte
res38: Byte = 127

scala> "128".toByte
java.lang.NumberFormatException: Value out of range. Value:"128" Radix:10
  at java.lang.Byte.parseByte(Byte.java:151)

scala> "1df28".toByte
java.lang.NumberFormatException: For input string: "1df28"
  at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
  at java.lang.Integer.parseInt(Integer.java:580)
  at java.lang.Byte.parseByte(Byte.java:149)
  at java.lang.Byte.parseByte(Byte.java:175)

scala> "200".toInt
res11: Int = 200

scala> "200".toInt * 3
res4: Int = 600

scala> 3 * "200".toInt 
res5: Int = 600

scala> 3 * "2ac00".toInt 
java.lang.NumberFormatException: For input string: "2ac00"
.... ...

scala> "100".toLong
res24: Long = 100

scala> "100fail!".toLong
java.lang.NumberFormatException: For input string: "100fail!"
  at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
  at java.lang.Long.parseLong(Long.java:589)
... ...

scala> "100".toFloat
res21: Float = 100.0

scala> "100a".toFloat
java.lang.NumberFormatException: For input string: "100a"
  at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:2043)
  at sun.misc.FloatingDecimal.parseFloat(FloatingDecimal.java:122)
  at java.lang.Float.parseFloat(Float.java:451)

scala> "300".toDouble
res7: Double = 300.0

scala> "300" toDouble
res8: Double = 300.0

scala> Math.log10("100".toDouble)
res10: Double = 2.0

scala> Math.log10("100It is gonna fail!".toDouble)
java.lang.NumberFormatException: For input string: "100It is gonna fail!"
  at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:2043)
  at sun.misc.FloatingDecimal.parseDouble(FloatingDecimal.java:110)
  at java.lang.Double.parseDouble(Double.java:538)
  at scala.collection.immutable.StringLike.toDouble(StringLike.scala:318)
  at scala.collection.immutable.StringLike.toDouble$(StringLike.scala:318)
  at scala.collection.immutable.StringOps.toDouble(StringOps.scala:29)
  ... 29 elided