Scala

****** Scala ******

Scala is a compiler based programming language
Build on funtional programing principles
Compiles into byte code
required jdk and jre
Seamless integeration with java


REPL - Read ,Evaluate ,print and loop
println("Hello world")
First it reads the code,then evaluate  which compile and produces byte code,print the output and loop which means it is waiting for next set of instructions
:quit
:help
ctrl+L will clear the screens
:history for history of the commands
:history 10
:save <path> to save the commands
:h? sc -> to search a keyword in history



**** Basic Programming constructs ****

Instead of giving each line in command line and executing ,we can execute a complete block of code.
Use :paste

and to run the block , ctrl+d

The disadvantage of using command line than paste mode is,
each line will be treated as a seperate program.e.,g

scala> val i = 10
i: Int = 10

scala> val i = "raj"
i: String = raj


In the above case,it allows i to be overwritten.

But in :paste mode,it wont allow us to overwwritte the value


--------------------

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

val i = 10
val i ="raj"

// Exiting paste mode, now interpreting.

<console>:8: error: i is already defined as value i
       val i ="raj"
           ^

--------------------



val : It is immutable...cannot be changed
var : mutable...it can be changed

e.g.,

val x: Int = 10
val t: String ="Raj"
val f: Float=10;
val b:Boolean = true;


The above values cannot be modified.

var t:Int = 12
var bool:Boolean=false

The above values can be modified

Type inference but not Dynamic typed

var d = true;
var s = "Raj";


We cannot change the type once it is assigned.You will get type mismatch error.e.g.,

-------------------------

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

var i = 1;
i = "Raj"

// Exiting paste mode, now interpreting.

<console>:9: error: type mismatch;
 found   : String("Raj")
 required: Int
       i = "Raj"
           ^


-------------------------

In scala,all arithmetich operations are functions. + , -, / ,*

scala> val i = 1 + 2
i: Int = 3

scala> val i = 1.+(2)
i: Int = 3

we can call the function as .+() . It is internally executed like this only

**** to get the list of functions supported for variable say i, we can type i.<tab> .It will list all functions.

------------------------------------


scala> i.
%   +   >    >>>            isInstanceOf   toDouble   toLong     unary_+   |   
&   -   >=   ^              toByte         toFloat    toShort    unary_-       
*   /   >>   asInstanceOf   toChar         toInt      toString   unary_~       

scala> val s= "Raj"
s: String = Raj

scala> s.
+                     concat             isInstanceOf         startsWith    
asInstanceOf          contains           lastIndexOf          subSequence   
charAt                contentEquals      length               substring     
chars                 endsWith           matches              toCharArray   
codePointAt           equalsIgnoreCase   offsetByCodePoints   toLowerCase   
codePointBefore       getBytes           regionMatches        toString      
codePointCount        getChars           replace              toUpperCase   
codePoints            indexOf            replaceAll           trim          
compareTo             intern             replaceFirst                       
compareToIgnoreCase   isEmpty            split                              

scala> s.
+              codePointBefore       concat             getBytes   isInstanceOf         regionMatches   startsWith    toString      
asInstanceOf   codePointCount        contains           getChars   lastIndexOf          replace         subSequence   toUpperCase   
charAt         codePoints            contentEquals      indexOf    length               replaceAll      substring     trim          
chars          compareTo             endsWith           intern     matches              replaceFirst    toCharArray                 
codePointAt    compareToIgnoreCase   equalsIgnoreCase   isEmpty    offsetByCodePoints   split           toLowerCase                 

scala> s.to
toCharArray   toLowerCase   toString   toUpperCase

scala> s.toUpperCase
res6: String = RAJ

-------------------------------------------

**** if you do not know the argument of any function you can click tab twice .It will list the function definitiion.

e.g., s.lastIndexOf<tab><tab>

-----------------------
scala> s.lastIndexOf
   def lastIndexOf(Int): Int   def lastIndexOf(Int, Int): Int   def lastIndexOf(String): Int   def lastIndexOf(String, Int): Int

-----------------------


****Collection

To create a collection in scala,we can just type (1 to 100).

scala> 1 to 100
res7: scala.collection.immutable.Range.Inclusive = Range(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100)

This has create a collection with res7 as reference.

To iterate over this collection, using for loop, then

scala> for (i <- 1 to 100) {
     | print(i)
     | }
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100

OR

scala> for (i <- 1 to 100) {
     | println(i)
     | }

 OR

scala> for (i <- res7){
     | print(i)
     | }
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100

OR

scala> res7.foreach(print)
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100


******* To get sum of all numbers using for loop

This is conventional approach

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

var sum = 0;
for(element <- 1 to 100){
sum =sum+element;
}

// Exiting paste mode, now interpreting.

sum: Int = 5050


****** to get sum of even number

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

var sum = 0;
for(element <- 1 to 100){
if(element % 2 == 0){
sum = sum+element;
}
}

// Exiting paste mode, now interpreting.

sum: Int = 2550



  Block of expression

With Semi colon (To write in a single line)

  scala> val x = {
     | val a = 100;
     | val b = 200;
     | a + b
     | }
x: Int = 300

Without semi colon (To write in multiple lines)


scala> val x = {
     | val a =1.3
     | val b =2.3
     | a * b
     | }
x: Double = 2.9899999999999998

Lazy Evaluation or on demand loading

scala> val x = 12;
x: Int = 12

scala> x * 10
res5: Int = 120

The above code allocates the memory and assign 12 to x.This is an issue because,This variable might be used in the program or not.

scala>  lazy val x =100;
x: Int = <lazy>

The above code does not allocates the memory.This is an issue because,The memory will be allocated during computation
scala> x * 2
res6: Int = 200

Another example

scala> val x = (1 to 1600000).toList
x: List[Int] = List(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159, 160, 161, 162, 163, 164, 165, 166, 167, 168, 169, 170, 171, 172, 173, 174, 175, 176, 177, ...
scala> x.reduce(_ + _)
res7: Int = 100545792

scala> lazy val x = (1 to 1600000).toList
x: List[Int] = <lazy>

scala> x.reduce(_ + _)
res8: Int = 100545792
 Lazy values are useful for delaying costly intizializtion instructions..

 Loop###

 scala> val str = "Test"
str: String = Test

scala> str.foreach(println)
T
e
s
t

scala> str.foreach(print)
Test

-- For each takes only a function

For Loop

syntax : for(arg  <- collection) code.....

scala> for (i <- 1 to 5) println(i)
1
2
3
4
5

The above prints 1 to 5

scala> for (i <- 5 to 1) println(i)

The above code does not print because,by default increemnt is one and If you want to print from 5 to 1..Do it as below,

scala> for (i <- 5 to 1 by -1) println(i)
5
4
3
2
1


More example,

scala> for (i <- 1 to 5) println(i)
1
2
3
4
5

scala> for (i <- 5 to 1) println(i)

scala> for (i <- 5 to 1 by -1) println(i)
5
4
3
2
1

scala> for (i <- 5 to 1 by -2) println(i)
5
3
1

scala> for (i <- 5 to 1 by -3) println(i)
5
2

scala> for (i <- 5 to 1 by 1) println(i)

scala> for (i <- 5 to 1 by -1) println(i)
5
4
3
2
1

scala> for (i <- 5 to 1 by -2) println(i)
5
3
1

scala> for (i <- 1 to 5 by 1) println(i)
1
2
3
4
5

scala> for (i <- 1 to 5 by 2) println(i)
1
3
5

scala> for(i <- 1 to 5; j <- 1 to 4) println(s"($i,$j)")
(1,1)
(1,2)
(1,3)
(1,4)
(2,1)
(2,2)
(2,3)
(2,4)
(3,1)
(3,2)
(3,3)
(3,4)
(4,1)
(4,2)
(4,3)
(4,4)
(5,1)
(5,2)
(5,3)
(5,4)

In the above code, $ is the substitue for i and j..which scala uses it.

scala> for ( i <- 1 to 5; j <- 1 to 4)
     | {
     | if(i == j)
     | println(s"($i,$j)")
     | }
(1,1)
(2,2)
(3,3)
(4,4)

The below code is  more efficient than above -> Gaurd function

scala> for (i <- 1 to 5; j <- 1 to 4 if i==j)
     | println(s"($i,$j)")
(1,1)
(2,2)
(3,3)
(4,4)


Yield

The result of each loop of iteration is stored in a List(Vector)

scala> for(i <- 1 to 20 if i % 2 == 0) yield(i)
res15: scala.collection.immutable.IndexedSeq[Int] = Vector(2, 4, 6, 8, 10, 12, 14, 16, 18, 20)

scala> val x = for(i <- 1 to 20 if i % 2 == 0) yield(i)
x: scala.collection.immutable.IndexedSeq[Int] = Vector(2, 4, 6, 8, 10, 12, 14, 16, 18, 20)

scala> x
res16: scala.collection.immutable.IndexedSeq[Int] = Vector(2, 4, 6, 8, 10, 12, 14, 16, 18, 20)

scala> x.foreach(print)
2468101214161820
scala> x.foreach(println)
2
4
6
8
10
12
14
16
18
20


function

syntax

def functioname(function param): returnType = {
    code....
}

def areaRect(l : Float.b :Float): Float = {
  l *b
}

scala> areaRect(2.3f,6.7f)
res22: Float = 15.409999

if you do not want return anything,then mention the return type as Unit
(like void in java)
scala> def areaRect(l:Float,b:Float):Unit = {
     | println(l)
     | }
areaRect: (l: Float, b: Float)Unit

*** Return type in the function not mandatory.Because the scala will either return the data or unit based on your pogram.It is intelligent enough to identify whether you function return or not

scala> areaRect(2.3f,6.7f)
2.3

scala> def isEvenNumber(number:Int):Boolean = {
     | number % 2 == 0
     | }
isEvenNumber: (number: Int)Boolean

scala> isEvenNumber(3)
res24: Boolean = false

scala> isEvenNumber(30)
res25: Boolean = true

scala> def isEvenNumber(number:Int):Boolean = {
     | if(number % 2 == 0 ) true
     | else false
     | }
isEvenNumber: (number: Int)Boolean

scala> isEvenNumber(30)
res26: Boolean = true

Default values can be set in the parameters of the function, as below.

scala> def areaRect(l:Int,b:Int):Int = { l*b }
areaRect: (l: Int, b: Int)Int

scala> areaRect(2,3)
res27: Int = 6

scala> def areaRect(l:Int,b:Int=10):Int = { l*b }
areaRect: (l: Int, b: Int)Int

scala> areaRect(2,3)
res28: Int = 6

scala> areaRect(2)
res29: Int = 20

scala> def areaRect(l:Int=12,b:Int):Int = { l*b }
areaRect: (l: Int, b: Int)Int

scala> areaRect(2,3)
res30: Int = 6

scala> areaRect(2)
<console>:9: error: not enough arguments for method areaRect: (l: Int, b: Int)Int.
Unspecified value parameter b.
              areaRect(2)
                      ^

scala> areaRect(b = 2)
res32: Int = 24


********Function passing function

Defining return type is optional

---------------------


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

def sum(func: Int => Int,lb :Int,ub:Int) = {
var total = 0;
for(element <- lb to ub){
 total = total + func(element)
}
total
}

// Exiting paste mode, now interpreting.

sum: (func: Int => Int, lb: Int, ub: Int)Int

scala> def id(i:Int) = i
id: (i: Int)Int

scala> def sqr(i:Int) = i*i
sqr: (i: Int)Int

scala> def cube(i:Int) = i*i*i
cube: (i: Int)Int

scala> def multOf100(i:Int) = i*100
multOf100: (i: Int)Int

scala> sum(id,1,10)
res0: Int = 55

scala> sum(sqr,1,10)
res1: Int = 385

scala> sum(cube,1,10)
res2: Int = 3025

scala> sum(multof100,1,10)
<console>:9: error: not found: value multof100
              sum(multof100,1,10)
                  ^

scala> sum(multOf100,1,10)
res4: Int = 5500


****** Anonymous functions **********

Anonymous functions
   can be assigned to variables
   can be passed as arguments to other functions

Anonymous function doesnt have any name.
We can pass as arguments to the othe function

e.g.,

--------------
i is the argument name = > is is the return type
scala> sum(i => i,1,10)
res5: Int = 55

scala> sum(i => i*i,1,10)
res6: Int = 385

scala> sum(i => i*i*i,1,10)
res7: Int = 3025

scala> sum(i => i*100,1,10)
res8: Int = 5500

scala> sum (i => {
     | if(i % 2 ==0) {
     | i*i
     | } else {
     | i * i * i
     | }
     | } , 1,10)

Data type is very important

scala> sum (i => {
     | if(i % 2 ==0) {
     | i*i
     | } else {
     | "Raj"
     | }
     | } , 1,10)
<console>:13: error: type mismatch;
 found   : String("Raj")
 required: Int
              "Raj"
              ^



-----------------
-------------------

Collections

Array

scala> val arr = new Array[Int](10)
arr: Array[Int] = Array(0, 0, 0, 0, 0, 0, 0, 0, 0, 0)

scala> arr(0) = 1

scala> arr(1) = 2

scala> arr(10) = 3
java.lang.ArrayIndexOutOfBoundsException: 10
  ... 33 elided

scala> arr(9) = 3

scala> arr
res41: Array[Int] = Array(1, 2, 0, 0, 0, 0, 0, 0, 0, 3)

scala> arr.foreach(println)
1
2
0
0
0
0
0
0
0
3

scala> val arr = new Array[String](10)
arr: Array[String] = Array(null, null, null, null, null, null, null, null, null, null)

scala> arr(0)
res43: String = null

scala> arr(0) = "Raj"

scala> arr(2) = "sekar"

scala> arr.foreach(println)
Raj
null
sekar
null
null
null
null
null
null
null

scala> val arr = Array(1,2,3,4)
arr: Array[Int] = Array(1, 2, 3, 4)

scala> arr.foreach(println)
1
2
3
4

//if an Object is declared as val,only the object reference becomes immutable and not the object value.hence you can change the value of the object.

e.g.,

scala> val arr = Array(1,2,3,4)
arr: Array[Int] = Array(1, 2, 3, 4)

scala> val arr1 = Array(1,2,3,4)
arr1: Array[Int] = Array(1, 2, 3, 4)

scala> arr = arr1
<console>:9: error: reassignment to val
       arr = arr1
           ^

scala> var arr = Array(1,2,3,4)
arr: Array[Int] = Array(1, 2, 3, 4)

scala> var arr1 = Array(1,2,3,4)
arr1: Array[Int] = Array(1, 2, 3, 4)

scala> arr = arr1
arr: Array[Int] = [I@720cbb7d


ArrayBuffer

scala> val arr = new ArrayBuffer[Int]()
<console>:7: error: not found: type ArrayBuffer
       val arr = new ArrayBuffer[Int]()
                     ^

scala> import scala.collection.mutable.ArrayBuffer
import scala.collection.mutable.ArrayBuffer

scala> val arr = new ArrayBuffer[Int]()
arr: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer()

scala> arr + = 200
<console>:12: error: missing arguments for method + in class any2stringadd;
follow this method with `_' if you want to treat it as a partially applied function
val $ires0 = arr.$plus
                 ^
<console>:9: error: reassignment to val
       arr + = 200
             ^

scala> arr += 200
res0: arr.type = ArrayBuffer(200)

scala> arr += 300
res1: arr.type = ArrayBuffer(200, 300)

scala> arr += (100,400,600)
res2: arr.type = ArrayBuffer(200, 300, 100, 400, 600)

scala> arr.foreach(arr)
java.lang.IndexOutOfBoundsException: 200
  at scala.collection.mutable.ResizableArray$class.apply(ResizableArray.scala:43)
  at scala.collection.mutable.ArrayBuffer.apply(ArrayBuffer.scala:48)
  at scala.collection.mutable.ArrayBuffer.apply(ArrayBuffer.scala:48)
  at scala.collection.mutable.ResizableArray$class.foreach(ResizableArray.scala:59)
  at scala.collection.mutable.ArrayBuffer.foreach(ArrayBuffer.scala:48)
  ... 33 elided

scala> arr.foreach(println)
200
300
100
400
600

scala> arr += Array(1000,4000,6000)
<console>:10: error: type mismatch;
 found   : Array[Int]
 required: Int
              arr += Array(1000,4000,6000)
                          ^

scala> arr ++= Array(1000,4000,6000)
res6: arr.type = ArrayBuffer(200, 300, 100, 400, 600, 1000, 4000, 6000)

scala> arr --= Array(1000,4000,6000)
res7: arr.type = ArrayBuffer(200, 300, 100, 400, 600)

scala> for(n <- arr) println(n)
200
300
100
400
600

scala> arr.foreach(println)
200
300
100
400
600

scala> for(n <- arr if n % 2 != 0) println(n)

scala> for(n <- arr if n % 2 = 0) println(n)
<console>:1: error: ')' expected but '=' found.
       for(n <- arr if n % 2 = 0) println(n)
                             ^

scala> for(n <- arr if n % 2 == 0) println(n)
200
300
100
400
600

scala> for(n <- arr if n % 2 == 0) yield(n)
res12: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(200, 300, 100, 400, 600)

scala> arr.filter(_ % 2 != 0).foreach(println)

scala> arr.filter(_ % 2 == 0).foreach(println)
200
300
100
400
600

scala> arr.max
res15: Int = 600

scala> arr.min
res16: Int = 100

scala> arr.max
res17: Int = 600

Maps

The below is the immutable map.Once created you cannot delete the key.

scala> val m = Map(1 -> "Binny", 2 -> "Stuart")
m: scala.collection.immutable.Map[Int,String] = Map(1 -> Binny, 2 -> Stuart)

scala> m -= 1
<console>:10: error: value -= is not a member of scala.collection.immutable.Map[Int,String]
              m -= 1
                ^

So,You need to create a mutable map

scala> import scala.collection.mutable.Map
import scala.collection.mutable.Map

scala> val m = Map(1 -> "Binny", 2 -> "Stuart")
m: scala.collection.mutable.Map[Int,String] = Map(2 -> Stuart, 1 -> Binny)

scala> m -= 1
res19: m.type = Map(2 -> Stuart)

scala> import scala.collection.mutable.Map
import scala.collection.mutable.Map

scala> val m = Map(1 -> "Binny", 2 -> "Stuart")
m: scala.collection.mutable.Map[Int,String] = Map(2 -> Stuart, 1 -> Binny)

scala> m -= 1
res19: m.type = Map(2 -> Stuart)

scala> m
res20: scala.collection.mutable.Map[Int,String] = Map(2 -> Stuart)

scala> m(1)
java.util.NoSuchElementException: key not found: 1
  at scala.collection.MapLike$class.default(MapLike.scala:228)
  at scala.collection.AbstractMap.default(Map.scala:59)
  at scala.collection.mutable.HashMap.apply(HashMap.scala:65)
  ... 33 elided

scala> m(2)
res22: String = Stuart

scala> m.get(1)
res23: Option[String] = None

scala> m.get(2)
res24: Option[String] = Some(Stuart)

scala>  m.getOrElse(1, "Raj")
res25: String = Raj

scala>  m
res26: scala.collection.mutable.Map[Int,String] = Map(2 -> Stuart)

scala>  m.getOrElse(10, 100)
res27: Any = 100

scala> m += (1 -> "Sekar")
res28: m.type = Map(2 -> Stuart, 1 -> Sekar)

scala> m
res29: scala.collection.mutable.Map[Int,String] = Map(2 -> Stuart, 1 -> Sekar)

mutable vs immutable collections