Scala Unified Types

Question 1

Any

Definition

Answer 1

Any is the supertype of all types, also called the top type. It defines certain universal methods such as equals, hashCode, and toString.

Question 2

Any’s direct subsclasses

Answer 2

AnyVal and AnyRef

Question 3

AnyVal

Definition

Answer 3

AnyVal represents value types

There are nine predefined value types and they are non-nullable.

Question 4

List 9 predefined value types

Answer 4

Double, Float, Long, Int, Short, Byte, Char, Unit, and Boolean

Question 5

AnyRef

Definition

Answer 5

AnyRef represents reference types

All non-value types are defined as reference types. Every user-defined type in Scala is a subtype of AnyRef. If Scala is used in the context of a Java runtime environment, AnyRef corresponds to java.lang.Object.

Question 6

Type casting

How value types are casted in Scala

Answer 6

• Byte -> Short -> Int -> Long -> Float -> Double
• Char -> Int

Question 7

Nothing

Definition

Answer 7

Nothing is a subtype of all types, also called the bottom type.

There is no value that has type Nothing. A common use is to signal non-termination such as a thrown exception, program exit, or an infinite loop (i.e., it is the type of an expression which does not evaluate to a value, or a method that does not return normally).

Question 8

Null

Definition

Answer 8

Null is a subtype of all reference types (i.e. any subtype of AnyRef). It has a single value identified by the keyword literal null.

Null is provided mostly for interoperability with other JVM languages and should almost never be used in Scala code. We’ll cover alternatives to null later in the tour.