Primitive and complex data types in Apex

Question

I am getting a little confused about which data types are primative and which are complex. The confusion really lies with only 1 or 2 of the data types. Below I have listed what I think is correct.

Primitive:

Blob, Boolean, Date, Datetime, Decimal, Double, ID, Integer, Long, Object (This one causes a little confusion as I believe sObject is complex but isn't Object the superclass of Sobject?), String

Complex:

Sobject, List, Set, Map, Enum

Is the above all correct? I understand that primitive data types are technically not primitive since they can be null and have methods so I am unsure what the defining characteristics are for a primitive and complex data type.

Answer 1

The distinction between primitives and non-primitives in Apex is, in my opinion, a bit fuzzier than it is in some languages. In particular, nullability and having methods does not distinguish primitives from non-primitives in Apex.

However, the documentation defines the Apex primitives as:

• Blob
• Boolean
• Date
• DateTime
• Decimal
• Double
• Id
• Integer
• Long
• Object
• String
• Time

Object, however, is a unique case insofar as it is the root of the type hierarchy in Apex (every data type is implicitly an Object, including sObjects and other primitives).

sObject itself is an abstract base class. You cannot construct a new, untyped sObject instance.

List, Set, and Map are parameterized collections. I think one can clearly define them as complex types.

enum itself is not a type; it's a keyword like class to create a new type. Enumerated types are Objects, however. If you were to do this in Anonymous Apex

public enum Test { VAL_ONE, VAL_TWO }
Test var = Test.VAL_ONE;
System.debug(var instanceof Object);

you'll get back an error saying

Operation instanceof is always true since an instance of Test is always an instance of Object

Answer 2

A primitive is an indivisible, immutable object, while a complex object contains other objects, both primitives and complex objects. Object itself is considered a primitive because you can't access the individual attributes of a complex object without casting first. SObject, by contrast, allows you to modify the individual fields in the record, as does List, Map, etc. Primitives also tend to have special treatment. For example, it's not possible to write an BigInteger class that behaves like a primitive (e.g. being able to write BigInteger i = 5;), but most primitives have special rules, and cannot generally be "constructed" directly (they always require factory methods or special syntax).

Answer 3

Primitive data types contain only one value, like 1, true, 1.23, 2023-01-02 etc. Non-primitive data types can contain multiple values or complex data like a set, list, map or a class and can be declared using the new keyword.