// Printing to console
System.out.println("Hello, World!");
// Hello, World!

int a = 1;
System.out.println("Hello world! " + a);
// Hello world! 1

// Reading input
import java.util.Scanner;

Scanner scanner = new Scanner(System.in);
System.out.print("Enter your name: ");
String name = scanner.nextLine();
System.out.println("Hello, " + name + "!");
// Enter your name: Sid
// Hello, Sid!

// Primitive Types
int age = 25;                  // Integer
double price = 19.99;          // Floating point
char grade = 'A';              // Character
boolean isStudent = true;      // Boolean

// Reference Types
String name = "Alice";         // String
Integer count = 10;            // Wrapper class
Double amount = 15.75;         // Wrapper class

// Arrays
int[] numbers = {1, 2, 3, 4, 5};
String[] names = new String[3];

// Constants
final double PI = 3.14159;

// Arithmetic operators
int sum = 5 + 3;       // 8
int diff = 5 - 3;      // 2
int product = 5 * 3;   // 15
int quotient = 5 / 2;  // 2 (integer division)
double result = 5.0 / 2.0; // 2.5
int remainder = 5 % 2; // 1

// Compound assignment
int number = 10;
number += 5;  // number = number + 5
number -= 3;  // number = number - 3
number *= 2;  // number = number * 2
number /= 4;  // number = number / 4

// Increment/decrement
int count = 0;
count++;      // count = count + 1
int prefixInc = ++count;  // increment first, then assign
int postfixInc = count++; // assign first, then increment

String name = "George";
if (name.equals("Debora")) {
    System.out.println("Hi Debora!");
} else if (name.equals("George")) {
    System.out.println("Hi George!");
}
// Hi George!

int x = 10;
if (x > 5) {
    System.out.println("Greater");
} else if (x == 5) {
    System.out.println("Equal");
} else {
    System.out.println("Smaller");
}
// Greater

// Basic switch
int day = 3;
switch (day) {
    case 1:
        System.out.println("Monday");
        break;
    case 2:
        System.out.println("Tuesday");
        break;
    case 3:
        System.out.println("Wednesday");
        break;
    default:
        System.out.println("Other day");
}
// Wednesday

// Switch expression (Java 14+)
String dayName = switch (day) {
    case 1 -> "Monday";
    case 2 -> "Tuesday";
    case 3 -> "Wednesday";
    case 4 -> "Thursday";
    case 5 -> "Friday";
    default -> "Weekend";
};
System.out.println(dayName); // Wednesday

// For loop
for (int i = 0; i < 3; i++) {
    System.out.println(i);
}
// 0
// 1
// 2

// Enhanced for loop (for-each)
String[] pets = {"Bella", "Milo", "Loki"};
for (String pet : pets) {
    System.out.println(pet);
}
// Bella
// Milo
// Loki

// While loop
int x = 3;
while (x > 0) {
    System.out.println(x);
    x--;
}
// 3
// 2
// 1

// Do-while loop
int y = 1;
do {
    System.out.println("Executed at least once: " + y);
    y++;
} while (y < 3);
// Executed at least once: 1
// Executed at least once: 2

// Continue - skips current iteration
for (int i = 0; i < 5; i++) {
    if (i == 2) {
        continue; // Skip when i is 2
    }
    System.out.println(i);
}
// 0
// 1
// 3
// 4

// Break - exits the loop
for (int i = 0; i < 5; i++) {
    if (i == 3) {
        break; // Exit loop when i is 3
    }
    System.out.println(i);
}
// 0
// 1
// 2

// String creation
String name = "Java";
String greeting = new String("Hello there!");

// String concatenation
String firstName = "John";
String lastName = "Doe";
String fullName = firstName + " " + lastName;
System.out.println(fullName); // John Doe

// StringBuilder for efficient string manipulation
StringBuilder sb = new StringBuilder();
sb.append("Hello");
sb.append(" ");
sb.append("World");
String result = sb.toString();
System.out.println(result); // Hello World

// String length
String text = "Hello";
System.out.println(text.length()); // 5

// String methods
String sentence = "java programming";
System.out.println(sentence.toUpperCase());        // JAVA PROGRAMMING
System.out.println(sentence.substring(0, 4));      // java
System.out.println(sentence.replace('a', 'o'));    // jovo progromming
System.out.println(sentence.contains("gram"));     // true
System.out.println(sentence.charAt(0));           // j

// String comparison
String s1 = "Hello";
String s2 = "hello";
System.out.println(s1.equals(s2));             // false
System.out.println(s1.equalsIgnoreCase(s2));   // true

// Basic method
public void sayHello(String name) {
    System.out.println("Hello " + name);
}

// Method with return value
public int add(int a, int b) {
    return a + b;
}

// Method with variable arguments
public double average(double... numbers) {
    double sum = 0;
    for (double num : numbers) {
        sum += num;
    }
    return numbers.length > 0 ? sum / numbers.length : 0;
}

// Method call examples
sayHello("Carlos");  // Hello Carlos
int sum = add(7, 8); // 15
double avg = average(1.0, 2.0, 3.0); // 2.0

// Method overloading - same name, different parameters
public void display(int number) {
    System.out.println("Integer: " + number);
}

public void display(String text) {
    System.out.println("String: " + text);
}

public void display(double number) {
    System.out.println("Double: " + number);
}

// Method calls
display(10);       // Integer: 10
display("Hello");  // String: Hello
display(5.5);      // Double: 5.5

import java.util.ArrayList;

// Creating ArrayList
ArrayList<String> names = new ArrayList<>();

// Adding elements
names.add("Alice");
names.add("Bob");
names.add("Charlie");

// Accessing elements
String firstName = names.get(0);  // Alice

// Modifying elements
names.set(1, "Robert");  // Replace "Bob" with "Robert"

// Removing elements
names.remove(2);  // Remove "Charlie"
names.remove("Alice");  // Remove by value

// Size of ArrayList
int size = names.size();

// Checking if empty
boolean isEmpty = names.isEmpty();

// Iterating through ArrayList
for (String name : names) {
    System.out.println(name);
}

// Clearing ArrayList
names.clear();

import java.util.HashMap;
import java.util.Map;

// Creating HashMap
HashMap<String, Integer> ages = new HashMap<>();

// Adding key-value pairs
ages.put("Alice", 25);
ages.put("Bob", 30);
ages.put("Charlie", 35);

// Accessing values
int aliceAge = ages.get("Alice");  // 25

// Checking if key exists
boolean hasKey = ages.containsKey("Bob");  // true

// Checking if value exists
boolean hasValue = ages.containsValue(40);  // false

// Removing entries
ages.remove("Charlie");

// Size of HashMap
int size = ages.size();

// Iterating through HashMap
for (Map.Entry<String, Integer> entry : ages.entrySet()) {
    System.out.println(entry.getKey() + ": " + entry.getValue());
}

// Iterating through keys
for (String key : ages.keySet()) {
    System.out.println(key);
}

// Iterating through values
for (Integer value : ages.values()) {
    System.out.println(value);
}

import java.util.HashSet;

// Creating HashSet
HashSet<String> fruits = new HashSet<>();

// Adding elements
fruits.add("Apple");
fruits.add("Banana");
fruits.add("Orange");
fruits.add("Apple");  // Duplicate, won't be added

// Size of HashSet
int size = fruits.size();  // 3 (no duplicates)

// Checking if element exists
boolean hasApple = fruits.contains("Apple");  // true

// Removing elements
fruits.remove("Banana");

// Iterating through HashSet
for (String fruit : fruits) {
    System.out.println(fruit);
}

// Clearing HashSet
fruits.clear();

import java.util.LinkedList;

// Creating LinkedList
LinkedList<String> list = new LinkedList<>();

// Adding elements
list.add("Apple");
list.add("Banana");
list.add("Orange");

// Special operations (besides ArrayList methods)
list.addFirst("First");           // Add at beginning
list.addLast("Last");            // Add at end
String first = list.getFirst();   // Get first element
String last = list.getLast();     // Get last element
list.removeFirst();              // Remove first element
list.removeLast();               // Remove last element

// Basic try-catch
try {
    int result = 10 / 0;  // Will throw ArithmeticException
    System.out.println("Result: " + result);
} catch (ArithmeticException e) {
    System.out.println("Error: Division by zero");
}

// Try-catch-finally
try {
    String text = null;
    System.out.println(text.length());  // Will throw NullPointerException
} catch (NullPointerException e) {
    System.out.println("Error: Null reference");
} finally {
    System.out.println("This will always execute");
}

// Multiple catch blocks
try {
    int[] numbers = new int[5];
    numbers[10] = 50;  // Will throw ArrayIndexOutOfBoundsException
} catch (ArrayIndexOutOfBoundsException e) {
    System.out.println("Error: Array index out of bounds");
} catch (Exception e) {
    System.out.println("Error: General exception");
}

// Throwing exceptions
public void checkAge(int age) {
    if (age < 0) {
        throw new IllegalArgumentException("Age cannot be negative");
    }
}

// Try-with-resources (Java 7+)
try (Scanner scanner = new Scanner(System.in)) {
    String input = scanner.nextLine();
    System.out.println("You entered: " + input);
} // Scanner will be automatically closed

// Class definition
public class Person {
    // Instance variables
    private String name;
    private int age;

    // Constructor
    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    // Default constructor
    public Person() {
        this.name = "Unknown";
        this.age = 0;
    }

    // Getters and setters
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        if (age >= 0) {
            this.age = age;
        }
    }

    // Method
    public void introduce() {
        System.out.println("Hi, I'm " + name + " and I'm " + age + " years old.");
    }

    // Static method
    public static Person createAdult(String name) {
        return new Person(name, 18);
    }
}

// Using the class
Person person1 = new Person("Alice", 25);
person1.introduce();  // Hi, I'm Alice and I'm 25 years old.

Person person2 = new Person();
person2.setName("Bob");
person2.setAge(30);
System.out.println(person2.getName());  // Bob

Person adult = Person.createAdult("Charlie");
adult.introduce();  // Hi, I'm Charlie and I'm 18 years old.

// Parent class
public class Animal {
    protected String name;

    public Animal(String name) {
        this.name = name;
    }

    public void makeSound() {
        System.out.println("Some generic animal sound");
    }
}

// Child class
public class Dog extends Animal {
    private String breed;

    public Dog(String name, String breed) {
        super(name);  // Call parent constructor
        this.breed = breed;
    }

    // Override parent method
    @Override
    public void makeSound() {
        System.out.println("Woof! Woof!");
    }

    // Additional method
    public void fetch() {
        System.out.println(name + " is fetching the ball!");
    }
}

// Using polymorphism
Animal myPet = new Dog("Buddy", "Golden Retriever");
myPet.makeSound();  // Woof! Woof!

// Type casting
if (myPet instanceof Dog) {
    Dog myDog = (Dog) myPet;
    myDog.fetch();  // Buddy is fetching the ball!
}

// Interface
public interface Drawable {
    void draw();  // Abstract method (no body)

    // Default method (Java 8+)
    default void display() {
        System.out.println("Displaying drawable object");
    }
}

// Abstract class
public abstract class Shape {
    protected String color;

    public Shape(String color) {
        this.color = color;
    }

    // Abstract method
    public abstract double calculateArea();

    // Concrete method
    public void displayColor() {
        System.out.println("Color: " + color);
    }
}

// Concrete class implementing interface and extending abstract class
public class Circle extends Shape implements Drawable {
    private double radius;

    public Circle(String color, double radius) {
        super(color);
        this.radius = radius;
    }

    @Override
    public double calculateArea() {
        return Math.PI * radius * radius;
    }

    @Override
    public void draw() {
        System.out.println("Drawing a " + color + " circle");
    }
}

// Using the classes
Circle circle = new Circle("Red", 5.0);
circle.draw();  // Drawing a Red circle
circle.display();  // Displaying drawable object
circle.displayColor();  // Color: Red
System.out.println("Area: " + circle.calculateArea());  // Area: 78.53981633974483