Data Types and Variables | Apex Developer Guide

Data Types
In Apex, all variables and expressions have a data type, such as sObject, primitive, or enum.

Primitive Data Types
Apex uses the same primitive data types as SOAP API, except for higher-precision Decimal type in certain cases.

Collections
Collections in Apex can be lists, sets, or maps.

Enums
An enum is an abstract data type with values that each take on exactly one of a finite set of identifiers that you specify. Enums are typically used to define a set of possible values that don’t otherwise have a numerical order. Typical examples include the suit of a card, or a particular season of the year.

Variables
Local variables are declared with Java-style syntax.

Constants
Apex constants are variables whose values don’t change after being initialized once. Constants can be defined using the final keyword.

Expressions and Operators
An expression is a construct made up of variables, operators, and method invocations that evaluates to a single value.

Assignment Statements
An assignment statement is any statement that places a value into a variable.

Rules of Conversion
In general, Apex requires you to explicitly convert one data type to another. For example, a variable of the Integer data type cannot be implicitly converted to a String. You must use the string.format method. However, a few data types can be implicitly converted, without using a method.