Data Types in Java

What is a Data Type?

A data type tells Java what kind of value a variable can store, such as numbers, decimal values, characters, or text.

Every variable in Java must have a data type before we can use it.

Example:

int age = 25;
String name = "John";
double salary = 25000.50;

Types of Data Types in Java

Java data types are divided into two categories:

1. Primitive Data Types
2. Non-Primitive Data Types

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1. Primitive Data Types

Primitive data types are the basic data types available in Java. They store simple values directly.

Java provides eight primitive data types.

Integer Types:

Data Type	Size	Description
byte	8 bits	Small whole numbers
short	16 bits	Short-range integers
int	32 bits	Commonly used for integers
long	64 bits	Large whole numbers

Floating-Point Types:

Data Type	Size	Description
float	32 bits	Decimal values
double	64 bits	More precise decimal values

Other Types:

Data Type	Size	Description
char	16 bits	Stores a single character
boolean	JVM-dependent	Stores true or false

Example:

int age = 25;
long population = 8000000L;

float price = 99.5f;
double salary = 25000.75;

char grade = 'A';
boolean isPassed = true;

Default Values of Primitive Data Types

When primitive variables are declared as class fields without assigning values, Java provides default values.

Data Type	Default Value
byte	0
short	0
int	0
long	0L
float	0.0f
double	0.0d
char	'\u0000'
boolean	false

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2. Non-Primitive Data Types

Non-primitive data types are used to store references to objects rather than directly storing simple values.

Some common examples are:

String

A String is used to store a sequence of characters (text).

String name = "Java";

Array

An array is used to store multiple values of the same data type in a single variable.

int[] numbers = {10, 20, 30, 40};

Class and Object

A class is a blueprint used to create objects. An object is an instance of a class.

Creating a Class:

class Student {
    String name;
    int age;
}

Creating an Object:

Student s1 = new Student();

s1.name = "John";
s1.age = 22;

Here, Student is the class, and s1 is the object created from that class.

Default Value of Non-Primitive Data Types

The default value of a non-primitive reference variable is null when declared as a class field without an assigned value.

Example:

class Student {
    String name;
    int age;
}

Here, the default value of name is null, and the default value of age is 0.

Note: Java provides default values for class fields, but local variables must be initialized before they are used.