Scala final ppt vinay

Introduction to
VINAY PORWAL
2013UCS032

Table of Contents
• Introduction
• Getting Started
• Features of Language
• Programming Environment
• Demo (Word Count with Spark, Simple Web App using Play, MongoDB,
ReactiveMongo)
• Resources
• Q&A 1

Introduction
2
•Object oriented and functional
•Statically typed - advanced type system
•Compiled to JVM bytecode
but also to CLR, and to JavaScript (in progress)
•High performance
•Very good interoperability with Java
•Support for modularity and extensibility
DSL friendly

History
3
The design of Scala started in 2001 at the (EPFL) by Martin
Odersky. Odersky formerly worked on Generic Java, and javac, Sun's
Java compiler.

May 2011, Odersky
launched Typesafe Inc.
Currently named
Lightbend Inc.
4

“Scala is an acronym for
Scalable Language ”
Is so named because it was designed to grow with the demands of its users.
6

Why a new Language?
The work on Scala was motivated
by two hypotheses:
Hypothesis 1: A general-purpose
language needs to be scalable; the
same concepts should describe
small as well as large parts.
Hypothesis 2: Scalability can be
achieved by unifying and
generalizing functional and object-
oriented programming concepts.
If we were forced to name just one aspect of Scala that helps scalability, we’d
pick its combination of object-oriented and functional programming.
7

What is Scala?
• Scala compiles to Byte Code in the JVM. Scala programs compile to JVM
bytecodes.Their run-time performance is usually on par with Java programs.
• You can write a .class being java or scala code.
• Interoperability with Java, So you can easily use the Java Ecosystem.
8

Why Scala?
• Scala is concise. No boilerplate code! (semicolons, return, getter/setter, …)
Fewer lines of code mean not only less typing, but also less effort at reading
and understanding programs and fewer possibilities of defects
• Scala is high-level. OOP and FP let you write more complex programs.
• Scala is statically typed, verbosity is avoided through type inference so it look
likes it’s a dynamic language but it’s not.
9

“
”
Even Apple needs Scala developer
12

If I were to pick a language to use today
other than Java, it would be Scala.
James Gosling, the creator of the Java programming language
“
”
13

Scala Use Cases
• Big Data and Data Science
• Web Application Development, REST API Development
• Distributed System, Concurrency and Parallelism
• Scientific Computation like NLP, Numerical Computing and Data
Visualization
14

They all use Scala
https://www.lightbend.com/resources/case-studies-and-storie 15

We’ve found that Scala has enabled us
to deliver things faster with less code.
GrahamTackley from TheGuardian.
“
”
16

Features of Language
• Scala Language Design
• The Basics of Scala
• Functional Programming in Scala
• Object-Oriented Programming in Scala
17

Scala Language Design
• ScalaType System
• Everything is an Expression
• Lexical scope
• Scopes
18

ScalaType System
Scala, unlike some of the other statically typed languages (C, Pascal, Rust,
etc.), does not expect you to provide redundant type information.You
don't have to specify a type in most cases, and you certainly don't have to
repeat it.
Scala has a unified type system, enclosed by the type Any at the top of the
hierarchy and the type Nothing at the
bottom of the hierarchy
19

ScalaType System
• Null: Its aTrait.
• null: Its an instance of Null- Similar to Java null.
• Nil: Represents an empty List of anything of zero length. Its
not that it refers to nothing but it refers to List which has no
contents.
• Nothing: is aTrait. Its a subtype of everything. But not
superclass of anything.There are no instances of Nothing.
• None: Used to represent a sensible return value. Just to avoid
null pointer exception. Option has exactly 2 subclasses- Some
and None. None signifies no result from the method.
• Unit: Type of method that doesn’t return a value of anys sort. 21

Everything is An Expression
In programming language terminology, an "expression" is a combination of values and functions
that are combined and interpreted by the compiler to create a new value, as opposed to a
"statement" which is just a standalone unit of execution and doesn't return anything
def ifThenElseExpression(aBool:Boolean) = if aBool then 42 else 0
22

Lexical Scope (Static)
• Scala using Lexical scoping like many other languages
(why?)
• Much easier for the user (programmer)
• Much easier for the compiler to optimize
23

Scopes
In a Scala program, an inner variable is said to shadow a like-named outer variable, because
the outer variable becomes invisible in the inner scope.
𝐿𝑜𝑐𝑎𝑙 𝐷𝑒𝑓𝑖𝑛𝑖𝑡𝑖𝑜𝑛𝑠 → 𝐸𝑥𝑝𝑙𝑖𝑐𝑖𝑡𝑠 𝑖𝑚𝑝𝑜𝑟𝑡𝑠 → 𝑊𝑖𝑙𝑑 𝑐𝑎𝑟𝑑 𝑖𝑚𝑝𝑜𝑟𝑡𝑠 → 𝑃𝑎𝑐𝑘𝑎𝑔𝑒𝑠
24

The Basics of Language
• DataTypes
• Casting
• Opperations
• If Expression
• Arrays &Tuples & Lists
• For & while Comprehension
• Functions
• Call By ...
• Pattern Matching
25

DataTypes
• Byte
• Short
• Int
• Long
• Float
• Double
• Char
• Boolean
• Unit
scala> var a:Int=2
a: Int = 2
scala> var a:Double=2.2
a: Double = 2.2
scala> var a:Float=2.2f
a: Float = 2.2
scala> var a:Byte=4
a: Byte = 4
scala> var a:Boolean=false
a: Boolean = false 26

Casting
• asInstanceOf
scala> var a:Char=(Char)955//Compile error
<console>:1: error: ';' expected but integer literal found.
var a:Char=(Char)955//Compile error
^
scala> var a:Int=955
a: Int = 955
scala> var b=a.asInstanceOf[Char]
b: Char = λ
27

Operations
scala> var a=955
a: Int = 955
scala> import scala.math._
import scala.math._
scala> print(4-3/5.0)
//compile time they will change to primitive not object any more to run faster 3.4
scala> print(a+3)//a.add(3) add=>+
958
scala> println(math.sin(4*Pi/3).abs)
//1)you can import classes 2)=>math.abs(math.sin(4*Pi/3))
0.8660254037844385
scala> if(a==955) | print("lambda")
Lambda
scala> println("HOLY".>=("EVIL"))
true
28

If Expression
scala> var m="wood"
m: String = wood
scala> println(m.length())
4
scala> println(s"$m is brown")
wood is brown
scala> println(f"$m%5s")
wood
scala> if(m=="wood"){//== is equivalent to equal
| print("brown");
| }else if(m.equals("grass")){
| println("green");
| }else{
| print("i don't know")
| }
brown
29

Arrays
scala> var arr=Array(5,4,47,7,8,7)
arr: Array[Int] = Array(5, 4, 47, 7, 8, 7)
scala> println(arr(1));println(arr(2));println(arr(3));
4 47 7
scala> var array=new Array[String](3);
array: Array[String] = Array(null, null, null)
scala> var at=Array(4,4.7,"Gasai Yuno")
at: Array[Any] = Array(4, 4.7, Gasai Yuno)
scala> var matrix=Array.ofDim[Int](2,2)
matrix: Array[Array[Int]] = Array(Array(0, 0), Array(0, 0))
30

Tuples
scala> var tuples=(2*5,"ten",10.0d,10.0f,10.0,(9,"NINE"))
tuples: (Int, String, Double, Float, Double, (Int, String)) =
(10,ten,10.0,10.0,10.0,(9,NINE))
scala> print(tuples._1)
10
scala> print(tuples._2)
ten
scala> print(tuples._6._2)
NINE
31

Lists
scala> var lst=List("b","c","d")
lst: List[String] = List(b, c, d)
scala> print(lst.head)
b
scala> print(lst.tail)
List(c, d)
scala> var lst2="a"::lst
lst2: List[String] = List(a, b, c, d)
scala> var l=1::2::3::4::Nil
l: List[Int] = List(1, 2, 3, 4)
scala> var l2=l::List(5,6)
l2: List[Any] = List(List(1, 2, 3, 4), 5, 6)
scala> var l3=l:::List(5,6)
l3: List[Int] = List(1, 2, 3, 4, 5, 6)
32

While
• while (Boolean Expression) { Expression }
• do { Expression } while (Boolean Expression)
scala> var i=0;
i: Int = 0
scala> while(i<10){
| i+=1;
| print(i+" ")
| }
1 2 3 4 5 6 7 8 9 10
Note : In functional , It is preferred to not use while and in general imperative style.
33

For Comprehension
• for (Iterations and Conditions)
val books = List("Beginning Scala", "Beginning Groovy",
"Beginning Java", "Scala in easy steps", "Scala in 24
hours")
for (book<-books)
println(book)
var scalabooks = for{ book <-books if
book.contains("Scala") }yield book
for(book<-books if book.contains("Scala") )
println(book)
34

foreach
 foreach (Conditions)
scala> val list = List("Human","Dog","Cat")
list: List[String] = List(Human, Dog, Cat)
scala> list.foreach((s : String) => println(s))
Human
Dog
Cat
scala> list.foreach(s => println(s))
Human
Dog
Cat
scala> list.foreach(println)
Human
Dog
Cat
35

Foreach vs For Comprehension
 Foreach VS for each
scala> for (s<- list) println(s)//it is actually
calling foreach
Human
Dog
Cat
scala> for(s<-list if s.length==3) println(s)
Dog
Cat
scala> list.foreach((s : String) => if(s.length()==3)
println(s))
Dog
Cat
36

Functions
scala> import scala.math._
import scala.math._
scala> def add(x:Int,y:Int):Int = {
| x+y//the last value if you dont specify return
|
| }
add: (x: Int, y: Int)Int
scala> def add(x:Double,y:Double) = x+y
add: (x: Double, y: Double)Double
Note: if you add “return” you need to specify return type else you are
not obligated and one line function no need to bracket.
37

Functions
scala> def printAdd(x:Int,y:Int){// no equal mark no return
| println(x+y)
| }
printAdd: (x: Int, y: Int)Unit
scala> def printAdd(x:Double,y:Double):Unit ={// Unit = void
| println(x+y)
| }
printAdd: (x: Double, y: Double)Unit
38

Functions
scala> def distance1(x1:Double,y1:Double,x2:Double,y2:Double):Double={
| def dif(x1:Double,x2:Double)={
| pow(x2-x1,2)
| }
| return sqrt(dif(x1,x2)+dif(y1,y2))
| }
distance1: (x1: Double, y1: Double, x2: Double, y2: Double)Double
scala> def
distance2(x1:Double,y1:Double,x2:Double,y2:Double,dif:(Double,Double)=>Double):Double={
| return sqrt(dif(x1,x2)+dif(y1,y2))
| }
distance2: (x1: Double, y1: Double, x2: Double, y2: Double, dif: (Double, Double) =>
Double)Double
39

Functions
scala> println(add(4.7,3.2))
7.9
scala> println(distance1(0, 0, 3, 0))
3.0
scala> var dif:(Double,Double)=>Double=(x:Double,y:Double)=>{pow(x-y,2)}
dif: (Double, Double) => Double = <function2>
scala> println(distance2(0, 0, 3, 0, dif))//unanonymous
3.0
scala> println(distance2(0, 0, 3, 0, (x:Double,y:Double)=>pow(x-y,2)))//anonymous
3.0
40

Tail Recursion
import scala.annotation.tailrec
// 1 - basic recursive factorial method
def factorial(n: Int): Int = {
if (n == 0) 1 else n * factorial(n-1)
}
// 2 - tail-recursive factorial method
def factorial2(n: Long): Long = {
@tailrec
def factorialAccumulator(acc: Long, n: Long): Long = {
if (n == 0) acc else factorialAccumulator(n*acc, n-1)
}
factorialAccumulator(1, n)
}
41

Call By Name
def delayed(t:=> Long) = {
println("Indelayed method")
println("Param:"+t)
t
}
42

Call By Ref
def notDelayed(t:Long) = {
println("Innotdelayed method")
println("Param:"+t)
t
}
Note : In Java, all method invocations are call-by-reference or call-
by-value (for primitive types) .
Scala gives you an additional mechanism for passing parameters to
methods (and functions):
call-by-name, which passes a code block to the callee. Each time the
callee accesses the parameter, the code
block is executed and the value is calculated. Call-by-name allows you
to pass parameters that might take a
longtime to calculate but may not be used. 43

Pattern Matching
scala> def matchChecking(a:Any):Unit={
| a match{
| case a:Int => {
| println("One");
| "ali"*5;
| }
| case "two" | "One" => {
| println("Two");
| 2*8;
| }
| case a if a<4.7 =>{
| println("four point seven");
| 3.8*2;
| }
| case _ => {
| println("Recognizing ...");
| a;
| }}}
matchChecking: (a: Any)Unit
scala> matchChecking(1);
One
44

Pattern Matching
scala> def simple_fun(list: List[Char]): List[Nothing] =
list match {
| case x :: xs => {
| println(x)
| simple_fun(xs)
| }
| case _ => Nil
| } simple_fun: (list: List[Char])List[Nothing]
scala> simple_fun(simplelist)
a
b
c
d
res22: List[Nothing] = List()
45

Functional Programming in Scala
• Lazy val & Eager Evaluation
• Currying
• Concurrency
• Closures
46

Lazy val & Eager Evaluation
 lazy val vs. val
The difference between them is, that a val is executed when it is
defined whereas a lazy val is executed when it is accessed the first
time.
In contrast to a method (defined with def) a lazy val is executed once
and then never again.This can be useful when an operation takes
long time to complete and when it is not sure if it is later used.
languages (like Scala) are strict by default, but lazy if explicitly
specified for given variables or parameters.
47

Currying
Methods may define multiple parameter lists.When a method is called
with a fewer number of parameter lists, then this will yield a function
taking the missing parameter lists as its arguments.
scala> def nDividesM(m : Int)(n : Int) = (n % m == 0)
nDividesM: (m: Int)(n: Int)Boolean
scala> val isEven = nDividesM(2)_
isEven: Int => Boolean = <function1>
scala> println(isEven(4))
true
Note : when you give only a subset of the parameters to the function,
the result of the expression is a partially applied function.
48

Closures
A closure is a function, whose return value depends on the value of
one or more variables declared outside this function.
scala> var votingAge = 18
votingAge: Int = 18
scala> val isVotingAge = (age: Int) => age >= votingAge
isVotingAge: Int => Boolean = <function1>
scala> isVotingAge(16)
res2: Boolean = false
49

Concurrency
• You have three options in concurrent programming:
• Akka Actor Model
• Thread
• Apache Spark
50

Actor
• Concurrency using threads is hard
• Shared state – locks, race conditions, deadlocks
• Solution – message passing + no shared state
• Inspired by Erlang language
• Erlang used at Ericsson since 1987, open source since
1998
• Facebook chat backend runs on Erlang
51

What is an Actor?
• Actor is an object that receives messages
• Actor has a mailbox – queue of incoming messages
• Message send is by default asynchronous
• Sending a message to an actor immediately returns
52

Object-Oriented Programming in Scala
• Classes
• Objects
• Traits
• Case Classes
• Exceptions
53

Classes
/** A Person class.
* Constructor parameters become
* public members of the class.*/
class Person(val name: String, var age: Int) {}
var p = new Person(“Peter", 21);
p.age += 1;
54

Objects
• Scala’s way for “statics”
• not quite – see next slide
• (in Scala, there is no static keyword)
• “Companion object” for a class
• = object with same name as the class
55

Objects
// we declare singleton object "Person"
// this is a companion object of class Person
object Person {
def defaultName() = "nobody"
}
class Person(val name: String, var age: Int) {
def getName() : String = name
}
// surprise, Person is really an object
val singleton = Person;
var p:Person=new Person(" ",0)
56

Case Classes
Implicitely override toString, equals, hashCode
take object’s structure into account
Usefull in pattern matching
abstract class Expr
case class Number(n: Int) extends Expr
case class Sum(e1: Expr, e2: Expr) extends Expr
// true thanks to overriden equals
Sum(Number(1), Number(2)) ==
Sum(Number(1), Number(2)) 57

Exceptions
object Main {
def main(args: Array[String]) {
try {
val elems = args.map(Integer.parseInt)
println("Sum is: " + elems.foldRight(0) (_ + _)) }
catch {
case e: NumberFormatException =>
println("Usage: scala Main <n1> <n2> ... ")
}
}
}
58

Traits
Like Java interfaces
But can contain implementations and fields
trait Pet {
var age: Int = 0
def greet(): String = {
return "Hi"
}
}
59

ExtendingTraits
class Dog extends Pet {
override def greet() = "Woof"
}
trait ExclamatoryGreeter extends Pet {
override def greet() = super.greet() + " !"
}
60

Mixins traits
Traits can be “mixed in” at instation time
trait ExclamatoryGreeter extends Pet {
override def greet() = super.greet() +
" !"
}
val pet = new Dog with ExclamatoryGreeter
println(pet.greet()) // Woof !
61

Scala has Multiple inheritance!!!
Solving the Diamond Problem
Scala’s solution to the Diamond Problem is actually fairly simple: it
considers the order in which traits are inherited. If there are multiple
implementors of a given member, the implementation in the supertype
that is furthest to the right (in the list of supertypes) “wins.” Of course, the
body of the class or trait doing the inheriting is further to the right than the
entire list of supertypes, so it “wins” all conflicts, should it provide an
overriding implementation for a member
62

Programming Environment
1. Download & Install JDK
2. Download & Install Scala http://www.scala-lang.org/download/.
3. Add the installed software to your environment
4. Type scala in Console
5. Have fun 
Note:You can download plugins in eclipse and intel and code 63

Resources
• http://www.scala-lang.org/files/archive/spec/2.12/
• https://www.tutorialspoint.com/scala/
• http://stackoverflow.com/tags/scala/info
• Beginning Scala
64

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