SCALA- PRACTICALS PART 3

 

Question: Calculate area of hall for 5 flats in a floor. 

       Solution: 

Suppose we have A building with 9th floor. And we have to calculate the area of 5 flat whose dimension are given below  

A-901 length len= 40.96, Width wid =20.00 

A-902 length len =35.84, Width wid =22.08 

A-903 length len =30.08, Width wid =16.00 

A-904 length len =45.50, Width wid =25.00 

A-905 length len =45.30, Width wid = 23.35 

Logic to find out the area of 5 flats of building whose dimensions are given: [len*wid]: logic 

 

Output: 

819.2 

788.48 

480.0 

1137.5 

964.355 

Process finished with exit code 0 

 

Note: without constructor, complier will never return any output  

• Default constructor  
• Primary constructor  
• Auxiliary constructor  

println is nothing it’s a by default constructor. 

constructor means it will print something. 

Step: of complier  

• Compiler try to find out where is main method  
• Reference for same class. 

Question: What is the difference between primary constructor and function? 

Answer:  

Primary constructor allows to perform encapsulation. 

Encapsulation has two points: It allows to perform getter and setter method. 

Getter: Try to access the value. It allows only access. Does not allow to change it. By default, immutable. Immutable means val. 

Setter: Setter can change and can change means mutable.

 

class Scala_Wel{ 
  def area(len:Double,wid:Double):Double ={ 
    val c = (len*wid) 
    println(c) 
  } 
} 
object Scal{ 
  def main(args: Array[String]):Double = { 
    val s1 = new Scala_Wel() 
    val s2 = new Scala_Wel() 
    val s3 = new Scala_Wel() 
    val s4 = new Scala_Wel() 
    val s5 = new Scala_Wel() 
    s1.area(40.96, 20.00) 
    s2.area(35.84, 22.00) 
    s3.area(30.00, 16.00) 
    s4.area(45.5, 25.00) 
    s5.area(41.3, 23.35) 
  } 
 
}

 

Classes, Functions and variables all these are by default public. 

when we don’t write in Scala by default 

No modifiers: by default, public 

modifiers:  

only the same class can access or the subclass can access or the same package can access. 

Types of modifiers:  

1. No modifier 

1. Private  

1. Protected 

What is the access pattern? 

• Outside package  
• Same package 

Modifiers
		Outside  Package	Same Package	Same Class	Sub Class	Companion Class
1	No Modifier	Yes	Yes	Yes	Yes	Yes
2	Private	No	No	Yes	No	Yes
3	Protected	No	No	Yes	Yes	Yes

 

• Singleton object: means there are no class only object. whenever we need to work with a static kind of concept. we want to implement once we don’t want to instantiate. It is used for static cases. 
• Companion class: class and object both have same name  

got to Scala class: kind it has class, case object, object, case object, trait. 

always we need a main method. Without main method compiler will never wake up. 

Extension of main method: extends App 

If we use extends App, then no need to type main method 

 

object Prop_Vol extends App { 
  //def main(args:Array[String]) ={} 
  println("Helli Scala") 
 
}

Helli Scala 

Process finished with exit code 0 

How to create a method:?  

def main(args:Array[String]): Unit  = { 

} 

main method cannot have more methods inside. We cannot write methods inside method  

For example:  

def main(args:Array[String]): Unit = { 

def vol ……….cannot write like this inside def function def vol  

} 

def cannot have inside def. 

Example of singleton object.  

The below example is for singleton. It’s a singleton object because there no class directly object 

 

object Prop_Vol  { 
   def main(args:Array[String])={ 
     def vol(l:Double,w:Double,h:Double)={ 
       (l*w*h) 
     } 
     println("This is vol of marriage hall"+vol(17.8,12.5,19.0)) 
  } 
 

 

 

This is vol of marriage hall4227.5 

Process finished with exit code 0 

How to instantiate Prop_Vol? 

 

object Prop_Vol  { 
   def main(args:Array[String])= { 
     println("This is vol of marriage hall"+vol(17.8,12.5,19.0)) 
   } 
  def vol(l:Double,w:Double,h:Double)= { 
    (l * w * h) 
   val p = new Prop_Vol() 
  } 
 
 
}

object Prop_Vol  { 
   def main(args:Array[String])= { 
     println("This is vol of marriage hall"+vol(17.8,12.5,19.0)) 
     val p = new Prop_Vol() 
  def vol(l:Double,w:Double,h:Double)= { 
    (l * w * h) 
   
  } 
 
 
} 

Page Break
 

Can not resolve symbol Pro_Vol 

object Prop_Vol  { 
   def main(args:Array[String])= { 
     println("This is for area1:"  +area(len =18.0f,wid= 16.5f)) 
     println("This is for area 2:" +area(len=20.0f,wid=18.2f)) 
   } 
  def area(len:Float,wid:Float) = { 
    (len*wid) 
  } 
}

This is for area1:297.0 

This is for area 2:364.0 

Process finished with exit code 0 

We cannot instantiate here we can just write a method a same object. But outside object it will get an issue. 

what are Scala class object case object, trait and Scala worksheet in intellij IDE and how to select for efficient programming  

Factorial function: 

Factorial function is recursion. recursive means function calling function. 

5! = 5*4*3*2*1 

logic  

n! =n*(n-1) *(n-2) *(n-3) ………………………………………………………….(n-n+1) 

How to use logic in syntax? 

Python logic for factorial, java logic for factorial, Scala logic for factorial. logic is same in all the languages only syntax is different  

 Fibonacci series :0,1, (0+1=1), (1+1=2), (1+2=3), (2+3=5), ………………… 

any recursive function needs return type. 

How write factorial methods in Scala  

Factorial without using class

object Prop_Vol  { 
   def main(args:Array[String])= { 
     println("output of factorial 5!:" +  facto(5)) 
   } 
   def facto(n:BigInt):BigInt = { 
     if(n==0)1 else n*facto(n-1) 
   } 
} 

output of factorial 5!:120 

Process finished with exit code 0 

object Prop_Vol  { 
   def main(args:Array[String])= { 
     println("output of factorial 10!:" +  facto(10)) 
   } 
   def facto(n:BigInt):BigInt = { 
     if(n==0)1 else n*facto(n-1) 
   } 
} 

output of factorial 10!:3628800 

Process finished with exit code 0 

object Prop_Vol  { 
   def main(args:Array[String])= { 
     println("output of factorial 6!:" +  facto(6)) 
   } 
   def facto(n:BigInt):BigInt = { 
     if(n==0)1 else n*facto(n-1) 
   } 
} 

 

output of factorial 6!:720 

Process finished with exit code 0 

object Prop_Vol  { 
   def main(args:Array[String])= { 
     println("output of factorial 3!:" +  facto(3)) 
   } 
   def facto(n:BigInt):BigInt = { 
     if(n==0)1 else n*facto(n-1) 
   } 
} 

output of factorial 3!:6 

Process finished with exit code 0

Factorial using class 

the factorial using class: in class we can write function within function then we can call it from my object . 

 

class Factorial_new { 
  def facto(n:BigInt):BigInt={ 
    if(n==0)1 else n*(n-1) 
  } 
} 
  object Prop_Vol1{ 
    def main(args:Array[String])={ 
      // create instantiation for class 
       val fn = new Factorial_new() 
       println(fn.facto(5)) 
    } 
 
  } 

20

 

Concept of Private:  

private can be accessible only an only within the class no outside 

private can be accessible only an only within the class no outside class Factorial_new { 
  private val n = 5 
  def facto(n:BigInt):BigInt = { 
    if(n==0)1 else n*facto(n-1) 
  } 
} 
  object Prop { 
    def main(args:Array[String])={ 
       val f = new Factorial_new() 
       f.n 
    } 
 
  } 

 

f.n: here symbol is inaccessible from this place . due to private it  can not be accessible outside the class. 

class Factorial_new { 
  private val n = 0; 
  def facto(n:BigInt):BigInt = { 
    if(n==0)1 else n*facto(n-1) 
  } 
} 
  object Prop { 
    def main(args:Array[String])={ 
       val f = new Factorial_new() 
       println(f.facto(6)) 
    } 
 
  } 

720

Concept of companion: 

Companion when class and object share the same names. 

class Factorial_new { 
  private val n = 0; 
  def facto(n:BigInt):BigInt = { 
    if(n==0)1 else n*facto(n-1) 
  } 
} 
  object Factorial_new { 
    def main(args: Array[String]) = { 
      val f = new Factorial_new() 
      println(f.n) 
    } 
  } 

0

Conditional expressions: 

• if  
• if else  

Whenever we want to use conditional expressions. Make sure that you are writing within the classes. 

and if you are creating a function you can write within the within the singleton object. 

if-else loop then you need to have a class.