Lesson 1: Java Basics

1. Variables and Data Types

What are Variables?

Variables are containers used to store data.

• In Java, every variable has a type that defines the kind of data it can hold.

Common Data Types in Java:

Data Type	Size	Description	Example
int	4 bytes	Stores integers	int age = 25;
double	8 bytes	Stores decimals	double price = 19.99;
char	2 bytes	Stores single characters	char grade = 'A';
String	Varies	Stores a sequence of characters	String name = "John";
boolean	1 bit	Stores true or false values	boolean isActive = true;

---

Code Example: Variables and Data Types

public class VariablesExample {
    public static void main(String[] args) {
        int age = 25; // Integer
        double price = 19.99; // Decimal
        char grade = 'A'; // Single character
        String name = "John"; // String
        boolean isActive = true; // Boolean

        System.out.println("Age: " + age);
        System.out.println("Price: " + price);
        System.out.println("Grade: " + grade);
        System.out.println("Name: " + name);
        System.out.println("Active: " + isActive);
    }
}

Expected Output:

Age: 25
Price: 19.99
Grade: A
Name: John
Active: true

---

2. Operators

Types of Operators in Java:

Operator	Description	Example
Arithmetic	Performs basic math	+, -, *, /, %
Relational	Compares two values	<, >, <=, >=, ==
Logical	Combines boolean conditions	&&, `
Assignment	Assigns values to variables	=, +=, -=, etc.

---

Code Example: Operators

public class OperatorsExample {
    public static void main(String[] args) {
        int a = 10, b = 20;

        // Arithmetic Operators
        int sum = a + b;
        int diff = b - a;

        // Relational Operators
        boolean isGreater = b > a;

        // Logical Operators
        boolean andCondition = (a < b) && (b > 15);

        System.out.println("Sum: " + sum);
        System.out.println("Difference: " + diff);
        System.out.println("Is b greater than a? " + isGreater);
        System.out.println("Logical AND Condition: " + andCondition);
    }
}

Expected Output:

Sum: 30
Difference: 10
Is b greater than a? true
Logical AND Condition: true

---

3. Input/Output

Taking Input from the User:

We use the Scanner class in Java to get input from the user.

---

Code Example: Input/Output

import java.util.Scanner; // Import Scanner class

public class InputOutputExample {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in); // Create Scanner object

        System.out.print("Enter your name: ");
        String name = scanner.nextLine(); // Read a String input

        System.out.print("Enter your age: ");
        int age = scanner.nextInt(); // Read an integer input

        System.out.println("Hello " + name + ", you are " + age + " years old.");
    }
}

Steps in NetBeans:

1. Create a new Java file named InputOutputExample.
2. Copy and paste the code above.
3. Run the program and interact with the console.

Sample Console Interaction:

Enter your name: John
Enter your age: 25
Hello John, you are 25 years old.