Declaration of Variables

In Java, declaring a variable means defining its data type and name. The basic syntax is as follows:

datatype variableName;

In this context, datatype indicates the type of data the variable will hold, such as int, double, boolean, or char, while variableName is the label used to reference the variable.

For example, let’s declare some variables:

int age;

double temperature;

boolean isRaining;

char grade;

Initialization of Variables

Initialization refers to the process of assigning a value to a variable. This can occur during the declaration or at a later point in the program:

int age = 25;

double temperature = 28.5;

boolean isRaining = true;

char grade = 'A';

Usage of Variables

Once a variable has been declared and initialized, it can be employed in various operations and calculations within the program:

int currentYear = 2024;

int birthYear = 1999;

int age = currentYear - birthYear;

System.out.println("Age: " + age);

double radius = 5.0;

double area = Math.PI * radius * radius;

System.out.println("Area of the circle: " + area);

boolean isAdult = age >= 18;

System.out.println("Is the person an adult? " + isAdult);

Scope of Variables

The scope of a variable defines where it can be accessed within the program. In Java, variables can be classified as either local or global.

Local Variables: These are declared within a method or a specific block of code and can only be accessed within that block.

void myMethod() {

int x = 10; // local variable

System.out.println(x);

}

Global Variables: Also known as instance or class variables, these are defined within a class but outside any method, allowing access throughout the class.

public class MyClass {

int y = 20; // global variable

void myMethod() {

System.out.println(y);

}

}