Immutable variables (val) and value types

Introduction to Scala

David Venturi

Curriculum Manager, DataCamp

The game of Twenty-One

¹ http://bit.ly/twenty_one_wikipedia

Scala has two kinds of variables

val (immutable)

• can't be reassigned

scala> val fourHearts: Int = 4

fourHearts: Int = 4

var (mutable)

Reassigning a val produces an error

scala> val fourHearts: Int = 4

fourHearts: Int = 4

scala> fourHearts = 5

<console>:12: error: reassignment to val
       fourHearts = 5
                  ^

Scala value types

• Double
• Float
• Long
• Int
• Short
• Byte
• Char
• Boolean
• Unit

Scala value types

Most common types for data-related tasks:

• Double
• Int
• Boolean
• String

Double

• 64-bit IEEE-754 double-precision floating point number
• 4.94065645841246544e-324d to 1.79769313486231570e+308d (positive or negative)

Double

scala> val piDouble: Double = 3.14

piDouble: Double = 3.14

Double

scala> val piFloat: Float = 3.14

<console>:11: error: type mismatch;
 found   : Double(3.14)
 required: Float
       val piFloat: Float = 3.14

Double is more precise than Float

scala> val piDouble: Double = 3.14159265358979323846264338327

piDouble: Double = 3.141592653589793

scala> val piFloat: Float = 3.14159265358979323846264338327f

piFloat: Float = 3.1415927

Int

• 32-bit signed integer
• -2^31 to 2^31-1, inclusive
• -2,147,483,648 to 2,147,483,647

Int

scala> val fourHearts: Int = 4

fourHearts: Int = 4

Boolean

• true or false

scala> val handBusts: Boolean = true

handBusts: Boolean = true

Char and String

Char

• 16-bit unsigned Unicode integer
• 0 to 2^16-1, inclusive
• 0 to 65,535

String

• String: a sequence of Char

Scala value types

• Double
• Float
• Long
• Int
• Short
• Byte
• Char
• Boolean
• Unit

Scala value types

• scala.Double
• scala.Float
• scala.Long
• scala.Int
• scala.Short
• scala.Byte
• scala.Char
• scala.Boolean
• scala.Unit

Scala value types

scala> val fourHearts: Int = 4

fourHearts: Int = 4

scala> val fiveHearts: scala.Int = 5

fiveHearts: Int = 5

Scala value types have equivalent Java types

Scala types

• scala.Double
• scala.Float
• scala.Long
• scala.Int
• scala.Short
• scala.Byte
• scala.Char
• scala.Boolean
• scala.Unit

Java types

• java.lang.Double
• java.lang.Float
• java.lang.Long
• java.lang.Integer
• java.lang.Short
• java.lang.Byte
• java.lang.Character
• java.lang.Boolean

Choosing the right type

• Double
• Float
• Long
• Int
• Short
• Byte
• Char
• Boolean
• Unit

Let's practice!

Introduction to Scala