17. జావా వారసత్వం (Inheritance), 'super' & Object Cosmic Superclass (Inheritance Mastery)

public class InheritanceConstructorExecutionDemo {

    // Level 1: Grandparent
    public static class HardwareDevice {
        String serialNumber;

        public HardwareDevice(String serial) {
            System.out.println("  1️⃣ [Executing HardwareDevice Constructor] Serial: " + serial);
            this.serialNumber = serial;
        }
    }

    // Level 2: Parent (extends HardwareDevice)
    public static class ComputingDevice extends HardwareDevice {
        int ramGigabytes;

        public ComputingDevice(String serial, int ram) {
            super(serial); // Explicit call to Grandparent constructor
            System.out.println("  2️⃣ [Executing ComputingDevice Constructor] RAM: " + ram + " GB");
            this.ramGigabytes = ram;
        }
    }

    // Level 3: Child (extends ComputingDevice)
    public static class CloudServerNode extends ComputingDevice {
        String regionZone;

        public CloudServerNode(String serial, int ram, String zone) {
            super(serial, ram); // Explicit call to Parent constructor
            System.out.println("  3️⃣ [Executing CloudServerNode Constructor] Zone: " + zone);
            this.regionZone = zone;
        }

        public void printSpecs() {
            System.out.printf("🖥️ Node Specs: Serial=%s | RAM=%d GB | Zone=%s%n",
                    serialNumber, ramGigabytes, regionZone);
        }
    }

    public static void main(String[] args) {
        System.out.println("=================================================");
        System.out.println("🏗️ INHERITANCE CONSTRUCTOR TOP-DOWN EXECUTION");
        System.out.println("=================================================
");

        System.out.println("Instantiating: new CloudServerNode('SRV-HYD-01', 64, 'ap-south-1a'):");
        CloudServerNode server = new CloudServerNode("SRV-HYD-01", 64, "ap-south-1a");

        System.out.println("
Final Initialized Object Specs:");
        server.printSpecs();

        System.out.println("
=================================================");
        System.out.println("✅ Top-Down Constructor Execution Flow Verified!");
        System.out.println("=================================================");
    }
}

import java.util.Objects;

public class ObjectClassContractDemo {

    // Overriding Object's core contracts properly
    public static class BankCustomer {
        private final String customerId;
        private final String panCard;
        private final String fullName;

        public BankCustomer(String id, String pan, String name) {
            this.customerId = id;
            this.panCard = pan;
            this.fullName = name;
        }

        @Override
        public String toString() {
            return "BankCustomer[ID=" + customerId + ", PAN=" + panCard + ", Name=" + fullName + "]";
        }

        @Override
        public boolean equals(Object obj) {
            if (this == obj) return true; // Reference check
            if (obj == null || getClass() != obj.getClass()) return false; // Type check

            BankCustomer other = (BankCustomer) obj;
            // Equality based on unique business key: customerId & panCard
            return Objects.equals(this.customerId, other.customerId) &&
                   Objects.equals(this.panCard, other.panCard);
        }

        @Override
        public int hashCode() {
            return Objects.hash(customerId, panCard);
        }
    }

    public static void main(String[] args) {
        System.out.println("=================================================");
        System.out.println("📜 JAVA.LANG.OBJECT CORE CONTRACTS AUDIT");
        System.out.println("=================================================
");

        BankCustomer c1 = new BankCustomer("CUST-101", "ABCDE1234F", "Balaji Nemani");
        BankCustomer c2 = new BankCustomer("CUST-101", "ABCDE1234F", "Balaji Nemani");
        BankCustomer c3 = new BankCustomer("CUST-102", "XYZPQ9876K", "Karthik Verma");

        // 1. toString() verification
        System.out.println("1. Clean toString() Output:");
        System.out.println("   c1: " + c1);

        // 2. equals() verification
        System.out.println("
2. equals() Logic:");
        System.out.println("   c1 == c2 (Reference Check):         " + (c1 == c2) + " (Distinct Heap Objects)");
        System.out.println("   c1.equals(c2) (Content Equivalence): " + c1.equals(c2) + " (Same Customer ID & PAN)");
        System.out.println("   c1.equals(c3):                       " + c1.equals(c3));

        // 3. hashCode() contract verification
        System.out.println("
3. hashCode() Contract:");
        System.out.println("   c1.hashCode(): " + c1.hashCode());
        System.out.println("   c2.hashCode(): " + c2.hashCode());
        System.out.println("   Contract Satisfied (c1.equals(c2) => same hash): " + (c1.hashCode() == c2.hashCode()));

        System.out.println("=================================================");
    }
}

import java.util.Objects;
import java.util.UUID;

public class FintechPaymentGatewayEngine {

    // Base Transaction Class (Superclass)
    public static class PaymentTransaction {
        private final String transactionId;
        private final double amount;
        private final String currency;
        private String status;

        public PaymentTransaction(double amount, String currency) {
            this.transactionId = "TXN-" + UUID.randomUUID().toString().substring(0, 8).toUpperCase();
            this.amount = amount;
            this.currency = currency;
            this.status = "INITIATED";
        }

        public void processPayment() {
            this.status = "SUCCESSFUL";
            System.out.printf("  💳 Base Payment [%s] Settled: %s %,.2f%n", transactionId, currency, amount);
        }

        public String getTransactionId() { return transactionId; }
        public double getAmount() { return amount; }
        public String getStatus() { return status; }

        @Override
        public String toString() {
            return String.format("[%s | %s %.2f | %s]", transactionId, currency, amount, status);
        }
    }

    // Subclass 1: Credit Card Payment Rail
    public static class CreditCardTransaction extends PaymentTransaction {
        private final String maskedCardNumber;
        private final String cardNetwork;

        public CreditCardTransaction(double amount, String currency, String cardNum, String network) {
            super(amount, currency); // Pass core fields to parent
            this.maskedCardNumber = "XXXX-XXXX-XXXX-" + cardNum.substring(cardNum.length() - 4);
            this.cardNetwork = network;
        }

        @Override
        public void processPayment() {
            System.out.println("🔒 Authorizing 3D Secure OTP with Card Network: " + cardNetwork);
            super.processPayment(); // Leverage parent settlement
            System.out.println("   └─► Card debited: " + maskedCardNumber);
        }
    }

    // Subclass 2: UPI Instant Payment Rail
    public static class UpiTransaction extends PaymentTransaction {
        private final String vpaAddress;
        private final String upiRefNumber;

        public UpiTransaction(double amount, String currency, String vpa) {
            super(amount, currency);
            this.vpaAddress = vpa;
            this.upiRefNumber = "UPI" + System.currentTimeMillis();
        }

        @Override
        public void processPayment() {
            System.out.println("⚡ NPCI Instant Switch Routing to VPA: " + vpaAddress);
            super.processPayment();
            System.out.println("   └─► Bank RRN Ref: " + upiRefNumber);
        }
    }

    public static void main(String[] args) {
        System.out.println("=================================================");
        System.out.println("💰 ENTERPRISE FINTECH PAYMENT GATEWAY PIPELINE");
        System.out.println("=================================================
");

        // Rail 1: Credit Card
        System.out.println("1. Processing Card Rail Transaction:");
        PaymentTransaction cardTxn = new CreditCardTransaction(45000.0, "INR", "4111222233339842", "VISA");
        cardTxn.processPayment();
        System.out.println("   Transaction Dossier: " + cardTxn + "
");

        // Rail 2: UPI Instant
        System.out.println("2. Processing UPI Rail Transaction:");
        PaymentTransaction upiTxn = new UpiTransaction(2500.0, "INR", "balaji@okaxis");
        upiTxn.processPayment();
        System.out.println("   Transaction Dossier: " + upiTxn);

        System.out.println("
=================================================");
        System.out.println("✅ All multi-rail transactions settled securely via Inheritance!");
        System.out.println("=================================================");
    }
}