Primitive and Non-Primitive Types

Java Core: Variables and Data Types - Primitive and Non-Primitive Types

In Java, every variable has a data type. This data type specifies the kind of value the variable can hold. Java data types are broadly categorized into two groups: Primitive Data Types and Non-Primitive Data Types (also known as Reference Data Types).

1. Primitive Data Types

• Definition: Primitive data types are the basic building blocks for representing data in Java. They directly store values. They are not objects.

• Characteristics:

  • Predefined by the Java language.
  • Fixed size (determined by the data type).
  • Stored directly in memory.
  • Faster to access and manipulate.
  • No methods associated with them.

• Types: Java has eight primitive data types:

  Data Type	Size (bits)	Range	Default Value	Description
  byte	8	-128 to 127	0	Represents small integer values.
  short	16	-32,768 to 32,767	0	Represents integer values (larger than byte).
  int	32	-2,147,483,648 to 2,147,483,647	0	Represents integer values.
  long	64	-9,223,372,036,854,775,808 to 9,223,372,036,854,775,807	0L	Represents large integer values.
  float	32	Approximately ±3.4028235e+38F	0.0F	Represents single-precision floating-point numbers.
  double	64	Approximately ±1.7976931348623157e+308	0.0	Represents double-precision floating-point numbers.
  boolean	1	true or false	false	Represents a logical value.
  char	16	Unicode character (0 to 65,535)	'\u0000'	Represents a single character.

• Example:

  int age = 30;
  double price = 19.99;
  boolean isStudent = true;
  char initial = 'J';
  

2. Non-Primitive Data Types (Reference Data Types)

• Definition: Non-primitive data types are created by the programmer. They are used to store complex data. They do not directly store values; instead, they store the memory address (reference) of the object.

• Characteristics:

  • Created by the programmer (or provided by Java libraries).
  • Variable size (depends on the object).
  • Stored in the heap memory.
  • Slower to access and manipulate compared to primitive types.
  • Have methods associated with them.
  • Can be null (meaning they don't point to any object).

• Types:

  • Classes: Blueprints for creating objects. (e.g., String, ArrayList, MyCustomClass)
  • Interfaces: Contracts that define a set of methods.
  • Arrays: Collections of elements of the same data type.
  • Enums: A special data type that enables a variable to be assigned a value from a predefined set of named constants.

• Example:

  String name = "John Doe"; // String is a class
  int[] numbers = {1, 2, 3, 4, 5}; // Array of integers
  // MyCustomClass is a user-defined class
  MyCustomClass myObject = new MyCustomClass();
  

• Important Note about Strings: Although String is often used like a primitive type, it's actually a class in Java. Therefore, it's a non-primitive type. String literals are often treated specially by the Java compiler for performance reasons (string interning), but they are still objects.

Key Differences Summarized

Understanding the difference between primitive and non-primitive data types is fundamental to writing efficient and correct Java code. Choosing the appropriate data type for a variable is crucial for memory management, performance, and overall program logic.