Variables and Data Types in Java

Variables and Data Types in Java

In Java, variables and data types are the fundamental concepts used to store and manage data in a program. Every application needs to store different kinds of information, such as names, ages, prices, marks, and other values. Java uses variables to store this information and data types to define what kind of values can be stored.

1. Variables in Java

A variable is a named memory location used to store data in a program. Every variable has a name, a data type, and a value.

Example:

String name = "Abimanyu";
int age = 21;
double salary = 25000.50;

System.out.println(name);
System.out.println(age);
System.out.println(salary);

Here, name, age, and salary are variables. Java allocates memory to store their values based on their data types.

Types of Variables

Java has three main types of variables:

• Local Variable: A variable declared inside a method, constructor, or block. It can only be accessed within its scope and must be initialized before use.
• Instance Variable: A variable declared inside a class but outside methods. Each object gets its own copy of these variables.
• Static Variable: A variable declared using the static keyword. It belongs to the class and is shared among its objects.

2. Data Types in Java

A data type defines what kind of value a variable can store. For example, an integer variable stores whole numbers, whereas a String variable stores text.

Java is a statically typed language, which means we must declare the data type when creating a variable.

Java data types are divided into two main categories:

Primitive Data Types

Primitive data types are the basic built-in data types provided by Java. Java has eight primitive data types.

Data Type	Size	Example
byte	8 bits	byte a = 100;
short	16 bits	short a = 2000;
int	32 bits	int a = 100;
long	64 bits	long a = 10000L;
float	32 bits	float a = 10.5f;
double	64 bits	double a = 20.55;
char	16 bits	char a = 'A';
boolean	JVM-dependent	boolean a = true;

Some important points:

• int is commonly used to store integer values.
• long is used for larger integer values.
• float and double are used for decimal values.
• char stores a single UTF-16 code unit.
• boolean stores either true or false.

Non-Primitive Data Types

Non-primitive data types are reference types used to work with objects and more complex data structures.

Some common examples are:

• String: Used to store a sequence of characters.
• Array: Used to store multiple values of the same type.
• Class: A blueprint used to create objects.

Example:

String name = "Abimanyu";

int[] marks = {85, 90, 95};

System.out.println(name);
System.out.println(marks[0]);

Unlike primitive types, reference variables can hold null, which means they do not currently refer to an object.

3. Type Casting in Java

Type casting is the process of converting one data type into another. Java supports two main types of casting.

Widening Casting (Automatic):

Converting a smaller compatible numeric type into a larger type.

int number = 100;

double result = number;

System.out.println(result);

Output: 100.0

Narrowing Casting (Manual):

Converting a larger numeric type into a smaller type. It requires explicit casting and may result in data loss.

double price = 99.99;

int result = (int) price;

System.out.println(result);

Output: 99