Scala Crash Course
Installation
First check whether if JAVA is installed on your linux machine
java --version
Install scala
sudo apt-get install scala
Start scala’s REPL
scala
If everything worked fine , something like this should appear in your terminal
Welcome to Scala 2.11.12 (OpenJDK 64-Bit Server VM, Java 11.0.7).
Type in expressions for evaluation. Or try :help.
scala>
Session 1
Use REPL for arithmetic calculation
Welcome to Scala 2.11.12 (OpenJDK 64-Bit Server VM, Java 11.0.7).
Type in expressions for evaluation. Or try :help.
scala> 60 + 9
res0: Int = 69
scala> 93 - 24
res1: Int = 69
scala> 13 * 5 + ( 32 / 8 )
res2: Int = 69
Const and Variables
- val : Immutable variable ( Read Only)
- var : mutable variable ( Read-Write)
scala> val x : Int = 10
x: Int = 10
scala> x = 11
<console>:12: error: reassignment to val
x = 11
^
scala> var x : Int = 10
x: Int = 10
scala> x =11
x: Int = 11
Data Types
scala> val x : Int = 10
x: Int = 10
scala> val x : String = "scala"
x: String = scala
scala> val x : Float =10f
x: Float = 10.0
scala> val x : Double = 10
x: Double = 10.0
scala> val x : Boolean = true
x: Boolean = true
- If we don’t write data type, scala automatically inferes the data type of variable not that doesn,t make it dynamically typed language instead it is called
Type Inference
Session 2
Data types in Scala
| Index |
Data Type |
Description |
| 1 |
Any |
Super type |
| 2 |
AnyVal |
Represent value type |
| 3 |
AnyRef |
Subtype of reference type |
| 4 |
Double |
64 bit float |
| 5 |
Float |
32 bit float |
| 6 |
Long |
64 bit signed value |
| 7 |
Int |
32 bit signed value |
| 8 |
Short |
16 bit signed value |
| 9 |
Byte |
8 bit signed value |
| 10 |
Unit |
Void |
| 11 |
Boolean |
True/False |
| 12 |
Char |
16 bit unsigned unicode |
| 13 |
Null |
Null |
| 14 |
Nothing |
Subtype of everytype |
Assigning Block Expression
scala> x * 2
res1: Int = 2000000
scala> val x = { 1 to 100000}.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(+)
res2: Int = 705082704
scala> lazy val x = { 1 to 100000}.toList
x: List[Int] =
scala> x.reduce(+)
res3: Int = 705082704
## Session 3
### `foreach` loop
```scala
scala> val str = "Test"
str: String = Test
scala> str.foreach(println)
T
e
s
t
for loop
scala> for ( i <- 1 to 5 ) println(i)
1
2
3
4
5
scala> 1 to 5
res2: scala.collection.immutable.Range.Inclusive = Range(1, 2, 3, 4, 5)
scala> for ( i <- 5 to 1 by -1 ) println(i)
5
4
3
2
1
scala> for ( i <- 1 to 5; j <- 1 to 4 ) println(s"($i, $j)")
(1, 1)
(1, 2)
(1, 3)
(1, 4)
(2, 1)
(2, 2)
(2, 3)
(2, 4)
(3, 1)
(3, 2)
(3, 3)
(3, 4)
(4, 1)
(4, 2)
(4, 3)
(4, 4)
(5, 1)
(5, 2)
(5, 3)
(5, 4)
if in for
- Inefficient way
scala> for ( i <- 1 to 5; j <- 1 to 4 ) if(i==j)println(s"($i, $j)")
(1, 1)
(2, 2)
(3, 3)
(4, 4)
- Efficient way (For loop with a guard condition)
```scala
scala> for ( i <- 1 to 5; j <- 1 to 4 if i==j)println(s”($i, $j)”)
(1, 1)
(2, 2)
(3, 3)
(4, 4)
scala> for ( i <- 1 to 20 if i % 2 == 0) println(i)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
res2: scala.collection.immutable.IndexedSeq[Int] = Vector(2, 4, 6, 8, 10, 12, 14, 16, 18, 20)
## Session 4
### Functions
* def **funcName**( **params**: type): return type {
**expression**
}
```scala
scala> def arearect(l: Float, b: Float): Float ={
| l * b
| }
arearect: (l: Float, b: Float)Float
scala> arearect(13, 17)
res0: Float = 221.0
- Use
Unit in return type if function doesn’t return anything i.e void function
```scala
scala> def areaRect(l: Float, b: Float): Unit ={
| println( l *b)
| }
areaRect: (l: Float, b: Float)Unit
scala> areaRect(40.5f, 3.5f)
141.75
* Boolean function
```scala
scala> def isEvenNumber(x: Int):Boolean ={
| x % 2 == 0
| }
isEvenNumber: (x: Int)Boolean
scala> isEvenNumber(9)
res2: Boolean = false
scala> isEvenNumber(8)
res3: Boolean = true
- Passing default arguments
scala> def areaRect(l: Int, b: Int = 10):Int = { l*b }
areaRect: (l: Int, b: Int)Int
scala> areaRect(10)
res4: Int = 100
- Overwriting default argument
```scala
scala> areaRect(10, 12)
res5: Int = 120
scala> def areaRect(l: Int = 10, b: Int):Int = { l*b }
areaRect: (l: Int, b: Int)Int
scala> areaRect(12)
:13: error: not enough arguments for method areaRect: (l: Int, b: Int)Int.
Unspecified value parameter b.
areaRect(12)
^
scala> areaRect(b = 12)
res7: Int = 120
scala> areaRect(12 , 10)
res8: Int = 120
```
## Session 5
### Arrays
* Int arrays
```scala
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
res2: Array[Int] = Array(1, 2, 0, 0, 0, 0, 0, 0, 0, 0)
scala> arr.foreach(println)
1
2
0
0
0
0
0
0
0
0
```
* String arrays
```scala
scala> val arr = new Array[String](10)
arr: Array[String] = Array(null, null, null, null, null, null, null, null, null, null)
scala> arr(0) = "0th Index"
scala> arr
res5: Array[String] = Array(0th Index, null, null, null, null, null, null, null, null, null)
```
### Buffer Array
```scala
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 += 100
res6: arr.type = ArrayBuffer(100)
scala> arr += 200
res7: arr.type = ArrayBuffer(100, 200)
scala> arr
res8: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(100, 200)
scala> arr += (300, 400, 500)
res9: arr.type = ArrayBuffer(100, 200, 300, 400, 500)
scala> arr ++= Array(300, 400, 500)
res11: arr.type = ArrayBuffer(100, 200, 300, 400, 500, 300, 400, 500)
scala> arr --= Array(300, 400, 500)
res12: arr.type = ArrayBuffer(100, 200, 300, 400, 500)
```
### Filter
```scala
scala> arr.filter( _ % 2 != 0 ).foreach(println)
scala> arr
res14: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(100, 200, 300, 400, 500)
```
### Sum, Min ans Max
```scala
scala> val arr = new Array [Int](3)
arr: Array[Int] = Array(0, 0, 0)
scala> arr(1) = 2
scala> arr(2) = 3
scala> arr(0) = 1
scala> arr
res5: Array[Int] = Array(1, 2, 3)
scala> arr.sum
res8: Int = 6
scala> arr.max
res9: Int = 3
scala> arr.min
res12: Int = 1
```
## Session 6
### List
``List in Scala are immutable``
* Int List
```scala
scala> val list = 1 :: 2 :: 3 :: Nil
list: List[Int] = List(1, 2, 3)
scala> val list = List(1, 2, 3)
list: List[Int] = List(1, 2, 3)
scala> val x = List(2)
x: List[Int] = List(2)
scala> list
res0: List[Int] = List(1, 2, 3)
scala> val y = 1 :: x
y: List[Int] = List(1, 2)
scala> val originalList = List(5, 1, 4, 3, 2)
originalList: List[Int] = List(5, 1, 4, 3, 2)
scala> val newList = originalList.filter(_>2)
newList: List[Int] = List(5, 4, 3)
scala> import scala.collection.mutable.ListBuffer
import scala.collection.mutable.ListBuffer
scala> val li = ListBuffer(1, 2, 3, 4, 5, 6, 7, 8, 9)
li: scala.collection.mutable.ListBuffer[Int] = ListBuffer(1, 2, 3, 4, 5, 6, 7, 8, 9)
scala> li.remove(0)
res2: Int = 1
scala> li
res3: scala.collection.mutable.ListBuffer[Int] = ListBuffer(2, 3, 4, 5, 6, 7, 8, 9)
scala> val li = List.range(0, 10, 2)
li: List[Int] = List(0, 2, 4, 6, 8)
scala> val li = List.fill(3)("w")
li: List[String] = List(w, w, w)
scala> val li = List.tabulate(5)(n => n + n)
li: List[Int] = List(0, 2, 4, 6, 8)
scala> val a = List(1, 2, 3)
a: List[Int] = List(1, 2, 3)
scala> val b = List(4, 5, 6)
b: List[Int] = List(4, 5, 6)
scala> val c = a ::: b
c: List[Int] = List(1, 2, 3, 4, 5, 6)
```
* String List
```scala
scala> var flowers = new ListBuffer[String]()
flowers: scala.collection.mutable.ListBuffer[String] = ListBuffer()
scala> flowers += "Rose"
res6: scala.collection.mutable.ListBuffer[String] = ListBuffer(Rose)
scala> flowers += "Tulip"
res7: scala.collection.mutable.ListBuffer[String] = ListBuffer(Rose, Tulip)
scala> flowers += "Lilly"
res8: scala.collection.mutable.ListBuffer[String] = ListBuffer(Rose, Tulip, Lilly)
scala> flowers
res10: scala.collection.mutable.ListBuffer[String] = ListBuffer(Rose, Tulip, Lilly)
scala> flowers --=Seq("Lilly")
res11: scala.collection.mutable.ListBuffer[String] = ListBuffer(Rose, Tulip)
scala> flowers
res12: scala.collection.mutable.ListBuffer[String] = ListBuffer(Rose, Tulip)
```
## Session 7
### Map
```scala
scala> val map = Map( 0 -> "OFF", 1 -> "ON" )
map: scala.collection.immutable.Map[Int,String] = Map(0 -> OFF, 1 -> ON)
scala> map
res13: scala.collection.immutable.Map[Int,String] = Map(0 -> OFF, 1 -> ON)
scala> map(1)
res14: String = ON
scala> map(32)
java.util.NoSuchElementException: key not found: 32
at scala.collection.MapLike$class.default(MapLike.scala:228)
at scala.collection.AbstractMap.default(Map.scala:59)
at scala.collection.MapLike$class.apply(MapLike.scala:141)
at scala.collection.AbstractMap.apply(Map.scala:59)
... 32 elided
scala> map.get(1)
res17: Option[String] = Some(ON)
```
* Hashtable/Map are always unordered and hence element can not be inserted in between.
## Session 8
### Tuples
```scala
tu: (Int, String, String) = (7,Bond,England)
scala> tu._1
res1: Int = 7
scala> tu._3
res2: String = England
```
## Session 9
### Sets
* These are also immutable by default
* These don't contain any duplicate elements
```scala
scala> var set = Set(1, 2, 3, 7)
set: scala.collection.immutable.Set[Int] = Set(1, 2, 3, 7)
scala> val set = Set(1, 1, 1, 2, 4, 5, 5)
set: scala.collection.immutable.Set[Int] = Set(1, 2, 4, 5)
scala> println("First element :" + set.head)
First element :1
scala> println("First element :" + set.tail)
First element :Set(2, 4, 5)
scala> println("Tail element :" + set.tail)
Tail element :Set(2, 4, 5)
scala> println("Is the set empty :" + set.isEmpty)
Is the set empty :false
scala> val set = Set("apples", "oranges", "pears")
set: scala.collection.immutable.Set[String] = Set(apples, oranges, pears)
scala> val fruit1 = Set("apples", "oranges", "pears")
fruit1: scala.collection.immutable.Set[String] = Set(apples, oranges, pears)
scala> val fruit2 = Set("apples", "oranges", "banana")
fruit2: scala.collection.immutable.Set[String] = Set(apples, oranges, banana)
scala> println( "Combined sets :" + (fruit1 ++ fruit2))
Combined sets :Set(apples, oranges, pears, banana)
```