Scala Type Hierarchy

Last Updated : 27 Feb, 2024

There are no primitive types in Scala(unlike Java). All data types in Scala are objects that have methods to operate on their data. All of Scala’s types exist as part of a type hierarchy. Every class that we define in Scala will also belong to this hierarchy automatically.

Any

Any is the superclass of all classes, also called the top class. It defines certain universal methods such as equals, hashCode, and toString. Any has two direct subclasses:

AnyVal
AnyRef

Example:

Scala

// Scala program of Scala Type hierarchy 
 
// Creating object
object Geeks 
{
 
    // Main method
    def main(args: Array[String]) 
    {
        val list: List[Any] = List(
                false,
                66677,
                732, 
                'a', 
                "abs"
                    )
 
        list.foreach(element => println(element))
    }
}

Output

false
66677
732
a
abs

AnyVal

AnyVal represents value classes. All value classes are predefined; they correspond to the primitive types of Java-like languages.

There are nine predefined value types and they are non-null able: Double, Float, Long, Int, Short, Byte, Char, Unit, and Boolean.
Scala has both numeric (e.g., Int and Double) and non-numeric types (e.g., String) that can be used to define values and variables.
Boolean variables can only be true or false. Char literals are written with single-quotes.
These are not nullable except Unit and all value classes are an abstract final type.

Example:

Scala

// Scala program of Scala Type hierarchy
// Using AnyVal. 
 
// Creating Object
object Geeks 
{
 
    // Main method
    def main(args: Array[String]) 
    {
        val list: List[AnyVal] = List(
            333, true, false
            )
 
        list.foreach(element => println(element))
    }
}

Output

333
true
false

Exception

Scala’s value types are much like Java’s primitive types except the Unit class.

Unit is a value type that does not carry any real information.
Unit class similar to Java’s Void type.
There exists a single instance of Unit that may be expressed literally in this manner: ().
Sometimes, functions need to return something, even nothing, so Unit comes in handy there.

AnyRef

AnyRef represents reference classes. All non-value types are defined as reference types.

In Scala, AnyRef is the root class of all reference types and child of “Any” class in the Scala type system.
These are types that refer to objects rather than directly holding values.
Every custom type in Scala belongs to AnyRef category.
User-defined classes define reference types by default; i.e. they always (indirectly) subclass scala.
AnyRef. scala.AnyRef in java programming corresponds to java.lang.Object.

Example:

Scala

// Scala program of Scala Type hierarchy 
// Using AnyRef
 
// Creating object
object Geeks
{
 
    // Main method
    def main(args: Array[String])
    {
        val list: List[AnyRef] = List(
        "GFG", "GEEKSFORGEEKS"
            )
 
        list.foreach(element => println(element))
    }
}

Output

GFG
GEEKSFORGEEKS

Nothing and Null

Nothing

Nothing is a subclassify of all value types, it is also called the bottom type. Type Nothing That has no value.

In Nothing you can’t create an instance of it or assign it to any variable.
It has zero instances.
One of the reasons to use Nothing is to provide a return type for the functions that never return i.e. a method which always throws an exception.
Nothing used as a return type for the operations that doesn’t return a value.
We can use Nothing to signal non-termination such as a thrown exception, program exit, or an infinite loop .

Null

Null is a subclassify of all reference types. the keyword literal null can identify a single value.

Null class is a child of all reference classes. But generally speaking, you should try to avoid using Null in typical Scala programming.
Using Scala’s literal keyword “null”, you can assign a Null to any reference class.
Null is provided mostly for interoperability with other JVM languages.