Wrapper Classes, Autoboxing & Enums Masterclass

public class WrapperDemo {
    public static void main(String[] args) {
        // Integer Utilities
        System.out.println("Integer Range: " + Integer.MIN_VALUE + " to " + Integer.MAX_VALUE);
        System.out.println("42 in Binary: " + Integer.toBinaryString(42));
        System.out.println("255 in Hex: " + Integer.toHexString(255));

        // Character Utilities
        char ch = '9';
        System.out.println("Is '" + ch + "' a digit? " + Character.isDigit(ch));
        System.out.println("Is 'A' uppercase? " + Character.isUpperCase('A'));

        // Double NaN and Infinity Check
        double zeroDiv = 10.0 / 0.0;
        System.out.println("10.0 / 0.0 = " + zeroDiv);
        System.out.println("Is Infinite? " + Double.isInfinite(zeroDiv));
    }
}

public class AutoboxingPitfalls {
    public static void main(String[] args) {
        // 1. Inside Cache Range (-128 to 127)
        Integer num1 = 127;
        Integer num2 = 127;
        System.out.println("num1 == num2 (127): " + (num1 == num2)); // true (Cached!)

        // 2. Outside Cache Range
        Integer num3 = 128;
        Integer num4 = 128;
        System.out.println("num3 == num4 (128): " + (num3 == num4)); // FALSE! (Different Heap references)
        System.out.println("num3.equals(num4):  " + num3.equals(num4)); // true (Correct comparison!)

        // 3. NullPointerException on Unboxing
        Integer nullWrapper = null;
        try {
            int primitiveVal = nullWrapper; // Compiles fine, but crashes at runtime!
        } catch (NullPointerException e) {
            System.out.println("⚠️ Caught NullPointerException: Cannot unbox null reference!");
        }
    }
}

public class ParsingDemo {
    public static void main(String[] args) {
        String ageStr = "25";
        String priceStr = "1299.75";
        String binaryStr = "1100100"; // 100 in binary

        // Parsing to numbers
        int age = Integer.parseInt(ageStr);
        double price = Double.parseDouble(priceStr);
        int decimalFromBinary = Integer.parseInt(binaryStr, 2);

        System.out.println("Age + 5 years: " + (age + 5));
        System.out.println("Price with 18% GST: Rs." + (price * 1.18));
        System.out.println("Binary 1100100 in Decimal: " + decimalFromBinary); // 100

        // Handling Invalid NumberFormatException safely
        String dirtyInput = "100Rs";
        try {
            int val = Integer.parseInt(dirtyInput);
        } catch (NumberFormatException e) {
            System.err.println("❌ Parsing Error: Input '" + dirtyInput + "' is not a valid number!");
        }
    }
}

// Rich Enum representing E-Commerce Order Status
enum OrderStatus {
    PENDING("Order received, awaiting payment", 101),
    PROCESSING("Items being packed in warehouse", 202),
    SHIPPED("Dispatched via courier delivery", 303),
    DELIVERED("Handed over to customer", 404),
    CANCELLED("Order cancelled and refunded", 505);

    // Custom Fields
    private final String description;
    private final int statusCode;

    // Enum Constructor (Always private or package-private)
    OrderStatus(String description, int statusCode) {
        this.description = description;
        this.statusCode = statusCode;
    }

    public String getDescription() { return description; }
    public int getStatusCode() { return statusCode; }

    public boolean isTerminalState() {
        return this == DELIVERED || this == CANCELLED;
    }
}

public class EnumDemo {
    public static void main(String[] args) {
        // 1. Iterating through all values()
        System.out.println("=== All Order Statuses ===");
        for (OrderStatus status : OrderStatus.values()) {
            System.out.println(status.ordinal() + ". " + status.name() + 
                               " [Code: " + status.getStatusCode() + "] -> " + status.getDescription());
        }

        // 2. Converting String to Enum with valueOf()
        String serverStatus = "SHIPPED";
        OrderStatus current = OrderStatus.valueOf(serverStatus);
        System.out.println("\nCurrent Order: " + current);
        System.out.println("Is order completed? " + current.isTerminalState());
    }
}

import java.util.Scanner;

enum MenuOption {
    CHECK_BALANCE(1, "Check Account Balance"),
    DEPOSIT_FUNDS(2, "Deposit Cash"),
    WITHDRAW_FUNDS(3, "Withdraw Cash"),
    EXIT(4, "Exit Application");

    private final int optionNumber;
    private final String label;

    MenuOption(int optionNumber, String label) {
        this.optionNumber = optionNumber;
        this.label = label;
    }

    public int getOptionNumber() { return optionNumber; }
    public String getLabel() { return label; }

    // Lookup Enum by entered number
    public static MenuOption fromNumber(int choice) {
        for (MenuOption opt : values()) {
            if (opt.optionNumber == choice) return opt;
        }
        return null; // Invalid option
    }
}

public class EnumMenuApp {
    private static double balance = 15000.00;

    public static void main(String[] args) {
        // Simulating menu choice 1 (Check Balance) and 2 (Deposit)
        processUserChoice(1);
        processUserChoice(2);
        processUserChoice(4);
    }

    public static void processUserChoice(int userChoice) {
        MenuOption selected = MenuOption.fromNumber(userChoice);

        if (selected == null) {
            System.out.println("❌ Invalid choice! Please select 1-4.");
            return;
        }

        // Modern Pattern Matching & Arrow Switch with Enums
        switch (selected) {
            case CHECK_BALANCE -> System.out.println("💰 Current Balance: Rs." + balance);
            case DEPOSIT_FUNDS -> {
                double depositAmt = 5000.0;
                balance += depositAmt;
                System.out.println("✅ Deposited Rs." + depositAmt + " | New Balance: Rs." + balance);
            }
            case WITHDRAW_FUNDS -> System.out.println("🏧 Processing withdrawal...");
            case EXIT -> System.out.println("👋 Thank you for banking with us. Goodbye!");
        }
    }
}