16. జావా ఎన్‌క్యాప్సులేషన్, Access Modifiers & రికార్డ్స్ (Encapsulation & Records)

public class EncapsulationValidationDemo {

    // 1. INSECURE CLASS: Public fields violate encapsulation
    public static class InsecureAccount {
        public String holder;
        public double balance; // Anyone can corrupt this directly!
    }

    // 2. SECURE CLASS: Strictly encapsulated with validation gates
    public static class SecureAccount {
        private String holder;
        private double balance;

        public SecureAccount(String holder, double initialDeposit) {
            this.setHolder(holder);
            this.setBalance(initialDeposit);
        }

        public String getHolder() {
            return holder;
        }

        public void setHolder(String holder) {
            if (holder == null || holder.trim().isEmpty()) {
                throw new IllegalArgumentException("Account holder name cannot be empty!");
            }
            this.holder = holder.trim();
        }

        public double getBalance() {
            return balance;
        }

        public void setBalance(double balance) {
            if (balance < 0.0) {
                System.out.printf("🚨 BLOCKED: Attempt to set negative balance (₹%.2f) rejected!%n", balance);
                return;
            }
            this.balance = balance;
        }
    }

    public static void main(String[] args) {
        System.out.println("=================================================");
        System.out.println("🛡️ ENCAPSULATION VIOLATION VS STRICT VALIDATION");
        System.out.println("=================================================
");

        // Vulnerability Demonstration
        InsecureAccount leaky = new InsecureAccount();
        leaky.holder = "Hacker Target";
        leaky.balance = -50000.0; // ❌ Invalid negative money entered directly!
        System.out.println("1. INSECURE ACCOUNT (No Protection):");
        System.out.println("   Holder: " + leaky.holder + " | Balance: ₹" + leaky.balance + " (CORRUPTED STATE!)");

        // Secure Encapsulated Demonstration
        System.out.println("
2. SECURE ENCAPSULATED ACCOUNT (Validation Gates):");
        SecureAccount safe = new SecureAccount("Balaji Nemani", 5000.0);
        System.out.println("   Initial Balance: ₹" + safe.getBalance());

        // Attempting to set illegal negative balance via setter
        System.out.println("   Attempting safe.setBalance(-25000.0)...");
        safe.setBalance(-25000.0);
        System.out.println("   Final Balance:   ₹" + safe.getBalance() + " (STILL SAFE & UNTOUCHED!)");

        System.out.println("
=================================================");
        System.out.println("✅ Encapsulation successfully prevented data corruption!");
        System.out.println("=================================================");
    }
}

public class ModernJavaRecordsDeepDiveDemo {

    // Modern Immutable Record with Compact Constructor
    public record DigitalProduct(String sku, String title, double price, int stockQuantity) {

        // Compact Constructor: No parameter list, auto-assigned after validation
        public DigitalProduct {
            if (sku == null || !sku.startsWith("DIG-")) {
                throw new IllegalArgumentException("SKU must start with 'DIG-': " + sku);
            }
            if (price < 0.0) {
                throw new IllegalArgumentException("Price cannot be negative: " + price);
            }
            title = title.trim(); // Clean input before implicit assignment
        }

        // Custom business method inside record
        public boolean isAvailable() {
            return stockQuantity > 0;
        }
    }

    public static void main(String[] args) {
        System.out.println("=================================================");
        System.out.println("⚡ MODERN JAVA 14+ RECORD DEEP DIVE DEMO");
        System.out.println("=================================================
");

        DigitalProduct ebook = new DigitalProduct("DIG-JAVA21", "Modern Java Masterclass", 499.00, 25);

        // 1. Automatic toString()
        System.out.println("1. Built-in toString():");
        System.out.println("   " + ebook);

        // 2. Direct component accessor methods (not getTitle(), just title())
        System.out.println("
2. Component Accessors:");
        System.out.println("   SKU:       " + ebook.sku());
        System.out.println("   Title:     " + ebook.title());
        System.out.println("   Price:     ₹" + ebook.price());
        System.out.println("   In Stock:  " + ebook.isAvailable());

        // 3. Built-in Value Equality (equals & hashCode)
        DigitalProduct identicalEbook = new DigitalProduct("DIG-JAVA21", "Modern Java Masterclass", 499.00, 25);
        System.out.println("
3. Equality Check (Value-based, not reference):");
        System.out.println("   ebook.equals(identicalEbook) ? " + ebook.equals(identicalEbook));
        System.out.println("   HashCode match: " + (ebook.hashCode() == identicalEbook.hashCode()));

        System.out.println("
=================================================");
        System.out.println("✅ Record handled all boilerplate with zero manual code!");
        System.out.println("=================================================");
    }
}

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class HealthcarePatientRecordEngine {

    // Modern Immutable Prescription Record
    public record MedicationPrescription(String drugName, String dosage, int durationDays) {
        public MedicationPrescription {
            if (drugName == null || drugName.isBlank()) throw new IllegalArgumentException("Drug name required");
            if (durationDays <= 0) throw new IllegalArgumentException("Duration must be at least 1 day");
        }
    }

    // Strictly Encapsulated Patient Medical File
    public static class PatientMedicalFile {
        private final String patientId;
        private String patientName;
        private int age;
        private double weightKg;
        // Mutable list protected via Defensive Copying
        private final List<MedicationPrescription> prescriptions;

        public PatientMedicalFile(String id, String name, int age, double weightKg) {
            if (id == null || !id.startsWith("PAT-")) {
                throw new IllegalArgumentException("Invalid Patient ID format (must start with PAT-): " + id);
            }
            this.patientId = id;
            this.setPatientName(name);
            this.setAge(age);
            this.setWeightKg(weightKg);
            this.prescriptions = new ArrayList<>();
        }

        public String getPatientId() {
            return patientId;
        }

        public String getPatientName() {
            return patientName;
        }

        public void setPatientName(String patientName) {
            if (patientName == null || patientName.trim().isEmpty()) {
                throw new IllegalArgumentException("Name cannot be blank");
            }
            this.patientName = patientName.trim();
        }

        public int getAge() {
            return age;
        }

        public void setAge(int age) {
            if (age < 0 || age > 120) throw new IllegalArgumentException("Invalid age boundary");
            this.age = age;
        }

        public double getWeightKg() {
            return weightKg;
        }

        public void setWeightKg(double weightKg) {
            if (weightKg <= 0.0) throw new IllegalArgumentException("Weight must be positive");
            this.weightKg = weightKg;
        }

        public void addPrescription(MedicationPrescription rx) {
            if (rx != null) {
                this.prescriptions.add(rx);
            }
        }

        // Defensive Copying: Returning an unmodifiable view to prevent external list tampering
        public List<MedicationPrescription> getPrescriptions() {
            return Collections.unmodifiableList(this.prescriptions);
        }

        public void printMedicalAudit() {
            System.out.println("-------------------------------------------------");
            System.out.println("🏥 APOLLO HEALTHCARE ELECTRONIC PATIENT DOSSIER");
            System.out.printf("Patient ID:   %s%n", patientId);
            System.out.printf("Full Name:    %s | Age: %d yrs | Weight: %.1f kg%n", patientName, age, weightKg);
            System.out.println("Active Prescriptions (" + prescriptions.size() + "):");
            for (MedicationPrescription rx : prescriptions) {
                System.out.printf("  💊 %-16s | Dosage: %-10s | Course: %d days%n",
                        rx.drugName(), rx.dosage(), rx.durationDays());
            }
            System.out.println("-------------------------------------------------");
        }
    }

    public static void main(String[] args) {
        System.out.println("=================================================");
        System.out.println("🩺 ENTERPRISE HEALTHCARE EMR & AUDIT ENGINE");
        System.out.println("=================================================
");

        PatientMedicalFile patient = new PatientMedicalFile("PAT-849201", "Balaji Nemani", 28, 74.5);

        // Adding immutable prescriptions
        patient.addPrescription(new MedicationPrescription("Amoxicillin", "500 mg", 5));
        patient.addPrescription(new MedicationPrescription("Paracetamol", "650 mg", 3));
        patient.addPrescription(new MedicationPrescription("Vitamin D3", "60,000 IU", 8));

        patient.printMedicalAudit();

        // Testing Defensive Copying Security
        System.out.println("Testing external tampering with patient.getPrescriptions()...");
        try {
            List<MedicationPrescription> externalList = patient.getPrescriptions();
            externalList.add(new MedicationPrescription("Illegal_Narcotic", "100 mg", 10)); // Should throw error!
        } catch (UnsupportedOperationException e) {
            System.out.println("🛡️ SECURITY ALERT BLOCKED: External code cannot modify patient prescription list!");
            System.out.println("   (Defensive Copying prevented unauthorized medical record tampering)");
        }

        System.out.println("
=================================================");
        System.out.println("✅ Healthcare dossier remains 100% verified and secure!");
        System.out.println("=================================================");
    }
}