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Variables

Variables are used to store data values that can be used and manipulated throughout the program. Each variable has a type that defines what kind of data it can hold.

Declaring Variables

Variables are declared by specifying their type followed by the variable name.

Where:

type refers to the data type of the variable.
variableName is the name of the variable you are declaring.
value is the initial value assigned to the variable (optional, but common when declaring variables).

Examples of declaring variables

int myInteger = 10; // Declares an integer variable

double myDouble = 3.14; // Declares a double variable

char myChar = 'A'; // Declares a char variable

boolean myBool = true; // Declares a boolean variable

byte myByte = 127; // Declares a byte variable

short myShort = 30000; // Declares a short variable

long myLong = 123456789L; // Declares a long variable (L suffix)

float myFloat = 5.75F; // Declares a float variable (F suffix)

String myString = "Hello, Java!"; // Declares a String variable

int[] myArray = {1, 2, 3}; // Declares an array variable

MyClass myObject = new MyClass(); // Declares an object of MyClass

Types of variables

Local Variables

Declared inside a method, constructor, or block.
Only accessible within that specific method or block.
Lifetime: Exists only while the method or block is executing.

public void display() {

int localVar = 10; // Local variable

System.out.println("Local Variable: " + localVar);

}

Instance Variables

Declared outside methods, but inside a class.
Belong to an object; each object gets its own copy.
Lifetime: Exists as long as the object exists.

public class Person {

String name; // Instance variable

public void setName(String name) {

this.name = name;

}

public void getName() {

System.out.println("Name: " + name);

}

Class (Static) Variables

Declared with the static keyword inside a class.
Belong to the class rather than any specific object.
Shared by all objects of the class.

public class Employee {

static int companyCode = 12345; // Class variable

public void displayCode() {

System.out.println("Company Code: " + companyCode);

}