Scala Essentials

Data Types in Scala

• A Data type tells the compiler about the type of the value to be stored in a location
• Scala comes with the following built-in data types which you can use for your Scala variables —

  Data Types in Scala (cont’d)

  Few examples

Variables Types in Scala

Variables are simply names used to refer to some location in memory – a location that holds a value with which we are working

Scala variables come in two shapes: Values and Variables

Values

Values: Immutable - “val” (Read only)

• Similar to Java Final Variables
• Once initialized, Vals can’t be reassigned —

  Variables:

  Mutable - “var” (Read-write) - Similar to non-final variables in Java

Here, myVar is declared using the keyword var. This means that it is a variable that can change value and this is called mutable variable —

Type Inference :

When you assign an initial value to a variable, the Scala compiler can figure out the type of the variable based on the value assigned to it This is called type inference Once a type is assigned to a variable, it remains same for entire scope

Thus, Scala is Statically Typed language

Assigning Block Expression

• In Java or C++ a code block is a list of statements in curly braces { }
• In Scala, a { } block is a list of expressions, and result is also an expression
• The Value of a block is the value of the last expression of it —

  Lazy Values

• One nice feature built into Scala are “lazy val” values.
• Lazy value initialization is deferred till it’s accessed for first time
• For example : If you want to read a file abc.txt, if the file is not existing , you will get FileNotFoundException exception —

  Lazy Values (cont’d)

• But if you initialize the value as Lazy, you won’t get this error, because it will delay the initialization till it accesses the file abc.txt

• Lazy values are very useful for delaying costly initialization instructions
• Lazy values don’t give error on initialization, whereas no lazy value do give error

Check your Understanding

If val a = (1, 2, 4,11, "Robert",5,9,11,2.5 ) then a._5?

1. No value , its wrong syntax
2. 5
3. Nil
4. “Robert”

Control Structures in Scala

• Control Structures controls the flow of execution
• Scala provides various tools to control the flow of program’s execution
• Some of them are

  if..else
  while
  do-while
  foreach
  for
  

  ---

  Control Structures in Scala (cont’d): if-else

  An if statement can be followed by an optional else statement, which executes when the boolean expression is false.

• if-else syntax in Scala is same as Java or C++
• In Scala, if-else has a value, of the expression following it
• Semicolons are optional in Scala —

  Control Structures in Scala (cont’d): if-else

  Every expression in Scala has a type. First If statement has a type Int Second statement has a type Any. Type of a mixed expression is supertype of both branches

Control Structures in Scala (cont’d): while loop

• A while loop statement repeatedly executes a target statement as long as a given condition is true
• In Scala while and do-while loops are same as Java —

  Control Structures in Scala (cont’d): do- While Loop

  A do…while loop is similar to a while loop, except that a do…while loop is guaranteed to execute at least one time Syntax: —

  Control Structures in Scala (cont’d): foreach Loop

  —

  Control Structures in Scala (cont’d): foreach Loop with function

  —

  Control Structures in Scala (cont’d): for loop

  for loop can execute a block of code for specific number of times. Scala doesn’t have for (initialize; test; update) syntax

  for( var x <- n ) {
  //Block of statements;
  }
  

  ---

  Scala: For Loop : to vs. until

  You can use either the keyword to or until when creating a Range object. The difference is, that to includes the last value in the range, whereas until leaves it out. Here are two examples: —

  Check your Understanding

  What is the output of the following program?

  for (x <- 'a' until 'f')
  print(x)
  

  1. Error
  2. abcde
  3. abcdef
  4. None of these

Control Structures in Scala: for Loop (cont’d)

Advanced For Loop: can have multiple generators in for loop

Control Structures in Scala: for Loop(cont’d)

We can put conditions in multi generators for loop

Control Structures in Scala: for Loop(cont’d)

We can introduce variables in loop!

Control Structures in Scala: The for Loop with Yield

If the body of for loop starts with yield, it returns a collection of values

val x = for(i<- 1 to 10) yield i*5

—

Functions

A function is a group of statements that together perform a task Scala function is a complete object which can be assigned to a variable The last statement in the function is the return value. You can create functions with “def” keyword

def functionName ([list of parameters]) : [return type] = {
    function body  
    return [expr]
}

—

Functions (cont’d)

We can provide defaults to function arguments, which will be used in case no value is provided in function calls

Functions (cont’d)

• We can specify argument names in function calls
• In named invocations the order of arguments is not necessary
• We can mix unnamed and named arguments, if the unnamed argument is the first one. We can specify argument names in function calls
• In named invocations the order of arguments is not necessary
• We can mix unnamed and named arguments, if the unnamed argument is the first one

• Scala supports variable number of arguments to a function

  Check your Understanding

  What is the output of the following?

def concatStr(a:String, b:Int=2 , c:String) = {a + b + c}
println(concatStr( "Hi",200, "Welcome"))

1. Hi2Welocme
2. Hi200Welcome
3. Error
4. Hi2200Welcome