Java Variables and Data Types

Variables are the fundamental building blocks of any program. In Java, a variable is a container that holds data which can be changed during the execution of the program.

Declaring and Initializing Variables

In Java, every variable must be declared with a specific data type. This tells the compiler how much memory to allocate and what kind of data can be stored.

Syntax:

dataType variableName = value;

Example:

int age = 25;
String name = "Saurabh";
double salary = 50000.50;

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Data Types in Java

Java is a statically-typed language, meaning all variables must be declared before they can be used. Data types are divided into two groups:

1. Primitive Data Types

These are predefined by the language and named by a reserved keyword. There are 8 primitive data types:

Type	Size	Description
byte	1 byte	Stores whole numbers from -128 to 127
short	2 bytes	Stores whole numbers from -32,768 to 32,767
int	4 bytes	Stores whole numbers from -2,147,483,648 to 2,147,483,647
long	8 bytes	Stores whole numbers for very large ranges (suffix with L)
float	4 bytes	Stores fractional numbers (suffix with f)
double	8 bytes	Stores fractional numbers (more precision than float)
boolean	1 bit	Stores true or false
char	2 bytes	Stores a single character/ASCII value (enclosed in ' ')

2. Non-Primitive (Reference) Data Types

These are created by the programmer and are not predefined by Java (except for String). Examples include:

• Strings: A sequence of characters. String greeting = "Hello";
• Arrays: Collections of data of the same type.
• Classes & Interfaces.

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Type Casting

Type casting is when you assign a value of one primitive data type to another type.

Widening Casting (Implicit)

Converting a smaller type to a larger type size. This happens automatically. byte -> short -> char -> int -> long -> float -> double

int myInt = 9;
double myDouble = myInt; // Automatic casting: int to double

Narrowing Casting (Explicit)

Converting a larger type to a smaller size type. This must be done manually. double -> float -> long -> int -> char -> short -> byte

double myDouble = 9.78d;
int myInt = (int) myDouble; // Manual casting: double to int

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Java Operators

Operators are used to perform operations on variables and values.

1. Arithmetic Operators

Operator	Name	Example
+	Addition	x + y
-	Subtraction	x - y
*	Multiplication	x * y
/	Division	x / y
%	Modulus	x % y (Returns division remainder)
++	Increment	++x
--	Decrement	--x

2. Relational (Comparison) Operators

Used to compare two values, returning a boolean.

• == (Equal to)
• != (Not equal)
• > (Greater than)
• < (Less than)
• >= (Greater than or equal)
• <= (Less than or equal)

3. Logical Operators

Used to determine the logic between variables or values.

• && (Logical and)
• || (Logical or)
• ! (Logical not)

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Next Steps

Now that you understand variables and data types, the next topic will cover Control Flow: If-Else, Switch, and Loops.