What are Variables?

Variables in Java are used to **store data** in memory. Each variable has a **data type**, a **name**, and a **value**.

Declaring Variables in Java

In Java, variables are declared using the syntax:

dataType variableName = value;

Example:

int age = 25;
double price = 99.99;
char grade = 'A';
String name = "John";

Types of Variables

• Local Variables: Declared inside a method and can only be used within that method.
• Instance Variables: Declared inside a class but outside methods. They belong to an object.
• Static Variables: Declared with the static keyword and shared among all instances of a class.

Data Types in Java

Java has two types of data types:

1. Primitive Data Types

These are the **basic data types** in Java:

• byte - 1 byte, stores small whole numbers (-128 to 127)
• short - 2 bytes, stores larger whole numbers
• int - 4 bytes, stores integers
• long - 8 bytes, stores large numbers
• float - 4 bytes, stores decimal numbers
• double - 8 bytes, stores large decimal numbers
• char - 2 bytes, stores a single character
• boolean - 1 byte, stores true or false

Example:

public class DataTypesExample {
    public static void main(String[] args) {
        int age = 30;
        double price = 50.5;
        char letter = 'A';
        boolean isJavaFun = true;

        System.out.println("Age: " + age);
        System.out.println("Price: " + price);
        System.out.println("Letter: " + letter);
        System.out.println("Is Java Fun? " + isJavaFun);
    }
}

2. Non-Primitive Data Types

These include **Strings, Arrays, Classes, and Interfaces.** They store references to objects.

Example:

public class NonPrimitiveExample {
    public static void main(String[] args) {
        String message = "Hello, Java!";
        int[] numbers = {1, 2, 3, 4, 5};

        System.out.println(message);
        System.out.println("First Number: " + numbers[0]);
    }
}

Type Casting in Java

Java allows conversion between different data types:

1. Implicit Casting (Widening Conversion)

Smaller data types can be converted to larger data types automatically.

int num = 100;
double newNum = num; // int to double (automatic)

2. Explicit Casting (Narrowing Conversion)

Larger data types must be manually converted to smaller types.

double price = 99.99;
int newPrice = (int) price; // double to int (manual)

Conclusion

Java provides a variety of data types for storing different kinds of values. Understanding variables and data types is essential for writing efficient Java programs.

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