Learning project SCALA

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rock-the-jvm-scala_rock-the-jvm-scala.iml

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rock-the-jvm-scala_src_lectures_Part1Basics_Expressions.scala

package lectures.Part1Basics

object Expressions extends App {

  val x = 1 + 2 //Expression
  println(x)

  println(2 + 3 * 4)
  // + - * / & | ^ << >> >>> (Right shift with zero extension)

  println(1 == 4)

  // == !=  < >= < <=

  println(!(1 == 4))
  // ! && ||

  var aVariable = 2
  aVariable +=3 //Also works -= *= /=
  println(aVariable)

  //Instructions vs Expressions

  //Instruction: Tell the comp. to do
  //Expression: Compute a value

  //IF expression: it gives a value.
  val aCondition = false
  val aConditionValue = if(aCondition) 5 else 3
  println(if(aCondition) 5 else 3)


  //DON'T DO THIS NEVER
  var i = 0
  while (i < 10) {
    println(i)
    i += 1
  }

  //EVERYTHING in Scala is an Expression!!

  val aWeirdValue = (aVariable = 3) //Unit === void

  //Side effects are expressions that return Unit!!!
  //println(), whiles, reassigning


  // Code blocks
  //Value of block is value of the last expression
  //Take care of visibility of vals
  val aCodeBlock = {
    val y = 2
    val z = y + 1

    if(z > 2) "hello" else "goodbye"
  }

  //1. Difference between "Hello world!" vs println("Hello world!")
  //"Hello world!" is a String type
  //println("Hello world!") is an expression that return a Unit value.

  //2.
  val someValue = {
    2 < 3
  }
  //This return true

  //3.

  val someOtherValue = {
    if(someValue) 239 else 986
    42
  }
  //This return 42


}

rock-the-jvm-scala_src_lectures_Part1Basics_Functions.scala

package lectures.Part1Basics

object Functions extends App {

  def aFuction(a: String, b: Int): String =
    a + " " + b

/*  def aFunction(a: String, b: Int): String = {
    a + " " + b
  }*/

  println(aFuction("Hello",3))

  def aParameterlessFunction(): Int = 42
  println(aParameterlessFunction())
  println(aParameterlessFunction)


  def aRepeatedFunction(aString: String, n: Int): String = {
    if (n == 1) aString
    else aString + aRepeatedFunction(aString, n-1)
  }

  println(aRepeatedFunction("Hello",3))

  //WHEN YOU NEED LOOPS, USE RECURSION.
  //In recursion we need to define return type of function.

  def aFunctionWithSideEffects(aString: String): Unit = println(aString)

  def aBigFunction(n: Int): Int = {
    def aSmallerFunction(a: Int, b: Int): Int = a + b

    aSmallerFunction(n, n-1)
  }

  /*
    1.  A greeting function (name, age) => "Hi, my name is $name and I am $age years old"
   */
  def greetingFunction(name: String, age:Int): String =
    "Hi, my name is " + name + " and I am " + age + " years old."
  /*
    2.  Factorial function
   */
  def factorialFunction(number: Int): Int =
    if(number <= 0) 1
    else number * factorialFunction(number-1)
  println(factorialFunction(5))

  /*
    3.  Fibonacci function
   */
  def fibonacciFunction(number: Int): Int =
    if (number == 1 || number == 2) 1
    else fibonacciFunction(number-1) + fibonacciFunction(number-2)
  println(fibonacciFunction(6))

  /*
    4.  Test if a number is prime
   */
  def isPrime(number: Int): Boolean = {
    def isPrimeUntil(t: Int): Boolean =
      if (t <= 1) true
      else number % t != 0 && isPrimeUntil(t-1)
    isPrimeUntil(number / 2)
  }
  println(isPrime(6))
  println(isPrime(37))
  println(isPrime(17))




}

rock-the-jvm-scala_src_lectures_Part1Basics_Recursion.scala

package lectures.Part1Basics

import java.security.KeyStore.TrustedCertificateEntry

import scala.collection.convert.StreamExtensions.AccumulatorFactoryInfo

object Recursion extends App {

  def factorialFunction(number: Int): Int =
    if(number <= 0) 1
    else {
      println("Computing factorial of " + number + " - I first need factorial of " + (number-1))
      val result = number * factorialFunction(number-1)
      println("Computed factorial of " + number)
      result
    }
  println(factorialFunction(5))

  def anotherFactorial(number: Int): BigInt = {
    def factorialHelper(x:Int, accumulator: BigInt):BigInt =
      if (x <= 1) accumulator
      else factorialHelper(x-1, x * accumulator) //TAIL RECURSION = use recursive call as the LAST expression.

    factorialHelper(number,1)
  }

  //WHEN YOU NEED LOOPS, USE _TAIL_ RECURSION

  /*
    1.  Concatenate a string n times
    2.  IsPrime function tail recursive
    3.  Fibonacci function tail recursive
   */

  /*
  1. Concatenate a string n times.
   */

  def stringConcatenator(str: String, times: Int): String = {
    def stringConcatenatorHelper(str: String, t: Int, result: String): String =
      if (t <= 0) result
      else stringConcatenatorHelper(str, t - 1, result + str)
    stringConcatenatorHelper(str,times,"")
  }
  println(stringConcatenator("Hello",5))

  def isPrime(number: Int): Boolean = {
    def isPrimeUntil(t: Int, isStillPrime: Boolean): Boolean =
      if (!isStillPrime) false
      else if (t <= 1) true
      else isPrimeUntil(t - 1,number % t != 0 && isStillPrime)
    isPrimeUntil(number/2, true)
  }

  def fibonacci(number: Int): Int = {
    def fibonacciHelper(n: Int, last: Int, nextToLast: Int): Int =
      if (n >= number) last
      else fibonacciHelper(n + 1, last + nextToLast, last)

    if (number <= 2) 1
    else fibonacciHelper(2, 1 ,1)
  }

}

rock-the-jvm-scala_src_lectures_Part1Basics_ValuesVariablesTypes.scala

package lectures.Part1Basics

object ValuesVariablesTypes extends App {

  //Vals

  val x: Int = 42
  println(x)

  //vals are immutable!!!
  //Type of vals are optional. Compiler can infer types

  val aString: String = "Hello!"
  val anotherString: String = "World!"

  val aBoolean: Boolean = false

  val aChar: Char = 'a'
  val anInt: Int = x
  val aShort: Short = 444
  val aLong: Long = 565465465654L //L at the end to mark that is a Long
  val aFloat: Float = 2.654f // f at the end to mark that is a Float
  val aDouble: Double = 3.14

  //Variables
  var aVariable: Int = 4

  //Mutable
  aVariable = 5 //Side effects



}

rock-the-jvm-scala_src_playground_JavaPlayground.java

package playground;

public class JavaPlayground {

    public static void main(String args[]) {
        System.out.println("Hello, Java world!");
    }
}

rock-the-jvm-scala_src_playground_ScalaPlayground.scala

package playground

object ScalaPlayground extends App {
    println("Hello Scala world!")
}