05. ఆపరేటర్లు, ఎక్స్‌ప్రెషన్స్ & టైప్ కాస్టింగ్ (Operators, Expressions & Type Casting)

public class ExpressionEvaluator {
    public static void main(String[] args) {
        System.out.println("==================================================");
        System.out.println("     COMPLEX EXPRESSION & PRECEDENCE EVALUATOR   ");
        System.out.println("==================================================");

        int a = 10;
        int b = 5;
        int c = 2;

        // Expression without parenthesis
        int result1 = a + b * c; // Multiplied first: 10 + 10 = 20
        // Expression with parenthesis overriding precedence
        int result2 = (a + b) * c; // Added first: 15 * 2 = 30

        System.out.printf("  10 + 5 * 2   = %d (Multiplication precedence)%n", result1);
        System.out.printf("  (10 + 5) * 2 = %d (Parentheses override)%n", result2);
        System.out.println("--------------------------------------------------");

        // Increment quirks demonstration
        int x = 5;
        int y = x++ + ++x; // 5 + 7 = 12, x becomes 7
        System.out.printf("  x = 5; x++ + ++x = %d (Final x = %d)%n", y, x);

        // Integer division vs floating division
        int intDiv = 10 / 4;
        double floatDiv = 10.0 / 4;
        System.out.printf("  10 / 4   (Integer)  = %d%n", intDiv);
        System.out.printf("  10.0 / 4 (Floating) = %.1f%n", floatDiv);
        System.out.println("==================================================");
    }
}

public class TypeCastingInspector {
    public static void main(String[] args) {
        System.out.println("--------------------------------------------------");
        System.out.println("       TYPE CASTING & OVERFLOW INSPECTION         ");
        System.out.println("--------------------------------------------------");

        // 1. Widening Casting (int to double) - 100% Safe
        int smallNumber = 450;
        double wideDouble = smallNumber;
        System.out.println("Widening (int → double): " + wideDouble);

        // 2. Narrowing Casting (double to int) - Truncates decimal part
        double productPrice = 1299.85;
        int truncatedPrice = (int) productPrice;
        System.out.println("Narrowing (1299.85 → int): " + truncatedPrice + " (Lost .85)");

        // 3. Overflow demonstration (byte range is -128 to 127)
        int largeVal = 130;
        byte overflowByte = (byte) largeVal; // Wraps around to negative!
        System.out.println("Overflow (130 → byte)    : " + overflowByte + " (Wrap-around!)");

        // 4. Bitwise Shift for ultra-fast multiplication and division
        int baseVal = 8;
        int multipliedByFour = baseVal << 2; // 8 * (2^2) = 32
        int dividedByTwo    = baseVal >> 1; // 8 / (2^1) = 4
        System.out.printf("Bitwise Shift: 8 << 2 = %d | 8 >> 1 = %d%n", multipliedByFour, dividedByTwo);
        System.out.println("--------------------------------------------------");
    }
}

public class EcommerceBillingEngine {
    public static void main(String[] args) {
        String itemName       = "Dell UltraSharp 27-inch 4K Monitor";
        int itemQuantity      = 2;
        double unitPriceUSD   = 350.00;
        double usdToInrRate   = 83.25;

        double discountPercentage = 15.0; // 15% Promotional Coupon
        double gstTaxPercentage   = 18.0; // 18% GST

        // Core Financial Equations
        double subtotalUSD = itemQuantity * unitPriceUSD;
        double discountUSD = (subtotalUSD * discountPercentage) / 100.0;
        double discountedUSD = subtotalUSD - discountUSD;
        double gstAmountUSD  = (discountedUSD * gstTaxPercentage) / 100.0;
        double finalTotalUSD = discountedUSD + gstAmountUSD;

        // Currency Conversion to INR via Type Casting
        double finalTotalINR = finalTotalUSD * usdToInrRate;
        long roundedTotalINR = Math.round(finalTotalINR);

        System.out.println("==================================================");
        System.out.println("      E-COMMERCE ORDER INVOICE & BILLING         ");
        System.out.println("==================================================");
        System.out.printf("  Item Name    : %s%n", itemName);
        System.out.printf("  Quantity     : %d units @ $%.2f USD each%n", itemQuantity, unitPriceUSD);
        System.out.println("--------------------------------------------------");
        System.out.printf("  Subtotal     : $%,10.2f USD%n", subtotalUSD);
        System.out.printf("  Discount 15%% : -$%,9.2f USD%n", discountUSD);
        System.out.printf("  GST Tax  18%% : +$%,9.2f USD%n", gstAmountUSD);
        System.out.println("--------------------------------------------------");
        System.out.printf("  TOTAL (USD)  : $%,10.2f USD%n", finalTotalUSD);
        System.out.printf("  EXCHANGE RATE: 1 USD = ₹ %.2f INR%n", usdToInrRate);
        System.out.printf("  TOTAL (INR)  : ₹ %,10d (Rounded)%n", roundedTotalINR);
        System.out.println("==================================================");
    }
}