15. జావా కన్‌స్ట్రక్టర్లు, 'this' కీవర్డ్ & Constructor Chaining (Constructors Mastery)

public class ConstructorOverloadingAndShadowingDemo {

    public static class DeviceProfile {
        String deviceId;
        String osType;
        int batteryPercent;

        // Broken constructor: Demonstrating Shadowing Bug
        public static DeviceProfile createWithShadowingBug(String deviceId, String osType) {
            DeviceProfile d = new DeviceProfile();
            // Variable shadowing occurs here: parameter reassigns to itself
            deviceId = deviceId;
            osType = osType;
            return d;
        }

        // Default no-arg constructor
        public DeviceProfile() {
            this.deviceId = "DEV-DEFAULT-001";
            this.osType = "Android-14";
            this.batteryPercent = 100;
        }

        // Overloaded constructor with 2 arguments (Correctly using this)
        public DeviceProfile(String deviceId, String osType) {
            this.deviceId = deviceId;
            this.osType = osType;
            this.batteryPercent = 100; // default battery
        }

        // Overloaded constructor with all 3 arguments
        public DeviceProfile(String deviceId, String osType, int batteryPercent) {
            this.deviceId = deviceId;
            this.osType = osType;
            this.batteryPercent = Math.min(100, Math.max(0, batteryPercent));
        }

        public void printProfile(String label) {
            System.out.printf("📱 [%-20s] ID: %-14s | OS: %-10s | Battery: %3d%%%n",
                    label, deviceId, osType, batteryPercent);
        }
    }

    public static void main(String[] args) {
        System.out.println("=================================================");
        System.out.println("🔧 CONSTRUCTOR OVERLOADING & SHADOWING DEMO");
        System.out.println("=================================================
");

        // 1. Using No-Arg Constructor
        DeviceProfile defaultDev = new DeviceProfile();
        defaultDev.printProfile("No-Arg Constructor");

        // 2. Using 2-Arg Constructor
        DeviceProfile customDev = new DeviceProfile("PIXEL-9-PRO", "Android-15");
        customDev.printProfile("2-Arg Constructor");

        // 3. Using 3-Arg Constructor
        DeviceProfile tabletDev = new DeviceProfile("IPAD-AIR-M2", "iPadOS-18", 78);
        tabletDev.printProfile("3-Arg Constructor");

        System.out.println("
=================================================");
        System.out.println("✅ All overloaded constructors executed with valid states!");
        System.out.println("=================================================");
    }
}

public class ConstructorChainingExecutionFlowDemo {

    public static class MicroserviceInstance {
        String serviceName;
        String environment;
        int maxReplicas;
        boolean enableTracing;

        // Constructor 1: No-arg (Calls Constructor 2)
        public MicroserviceInstance() {
            this("AuthService"); // Chaining to 1-arg
            System.out.println("  1️⃣ [Exiting Constructor 1: No-arg]");
        }

        // Constructor 2: 1-arg (Calls Constructor 3)
        public MicroserviceInstance(String name) {
            this(name, "DEVELOPMENT"); // Chaining to 2-arg
            System.out.println("  2️⃣ [Exiting Constructor 2: 1-arg ('" + name + "')]");
        }

        // Constructor 3: 2-args (Calls Master Constructor 4)
        public MicroserviceInstance(String name, String env) {
            this(name, env, 3, false); // Chaining to Master 4-arg
            System.out.println("  3️⃣ [Exiting Constructor 3: 2-args ('" + name + "', '" + env + "')]");
        }

        // Master Constructor 4: Performs actual assignment
        public MicroserviceInstance(String name, String env, int replicas, boolean tracing) {
            System.out.println("  4️⃣ [Executing Master Constructor 4 (Core Initialization)]");
            this.serviceName = name;
            this.environment = env;
            this.maxReplicas = replicas;
            this.enableTracing = tracing;
        }

        public void printTelemetry() {
            System.out.printf("🚀 Service: %-14s | Env: %-12s | Replicas: %d | Tracing: %b%n",
                    serviceName, environment, maxReplicas, enableTracing);
        }
    }

    public static void main(String[] args) {
        System.out.println("=================================================");
        System.out.println("🔗 CONSTRUCTOR CHAINING EXECUTION FLOW TRACER");
        System.out.println("=================================================
");

        System.out.println("Initiating: new MicroserviceInstance():");
        MicroserviceInstance svc = new MicroserviceInstance();

        System.out.println("
Final Initialized State:");
        svc.printTelemetry();

        System.out.println("
=================================================");
        System.out.println("✅ Master Constructor executed first, then callers in reverse!");
        System.out.println("=================================================");
    }
}

public class CloudDatabasePoolManagerEngine {

    public static class ConnectionPoolConfig {
        // Core Configuration Properties
        private final String poolName;
        private final String jdbcUrl;
        private final int minConnections;
        private final int maxConnections;
        private final int connectionTimeoutMs;
        private final boolean isSslRequired;

        // Constructor 1: Quick Dev Profile (Chains to Constructor 2)
        public ConnectionPoolConfig() {
            this("DevLocalPool", "jdbc:postgresql://localhost:5432/app_db");
        }

        // Constructor 2: Standard Profile (Chains to Master Constructor 3)
        public ConnectionPoolConfig(String poolName, String jdbcUrl) {
            this(poolName, jdbcUrl, 5, 20, 30000, true);
        }

        // Constructor 3: Master Fully-Parameterized Constructor with Strict Validation
        public ConnectionPoolConfig(String poolName, String jdbcUrl,
                                    int minConn, int maxConn, int timeoutMs, boolean ssl) {
            if (minConn < 0 || maxConn < minConn) {
                throw new IllegalArgumentException("Invalid pool boundaries: min must be >= 0 and max >= min");
            }
            this.poolName = poolName;
            this.jdbcUrl = jdbcUrl;
            this.minConnections = minConn;
            this.maxConnections = maxConn;
            this.connectionTimeoutMs = timeoutMs;
            this.isSslRequired = ssl;
        }

        // Constructor 4: Copy Constructor (Defensive Snapshot)
        public ConnectionPoolConfig(ConnectionPoolConfig source) {
            this(source.poolName + "_ReplicaSnapshot",
                 source.jdbcUrl,
                 source.minConnections,
                 source.maxConnections,
                 source.connectionTimeoutMs,
                 source.isSslRequired);
        }

        public void printAuditReport() {
            System.out.println("-------------------------------------------------");
            System.out.println("🛡️ CLOUD DATABASE POOL TELEMETRY SPECIFICATION");
            System.out.printf("Pool Name:       %s%n", poolName);
            System.out.printf("JDBC URL:        %s%n", jdbcUrl);
            System.out.printf("Connection Band: Min: %d | Max: %d (Scale Factor: %.1fx)%n",
                    minConnections, maxConnections, (double) maxConnections / Math.max(1, minConnections));
            System.out.printf("Timeout Window:  %d ms | SSL Encrypted: %b%n", connectionTimeoutMs, isSslRequired);
            System.out.println("-------------------------------------------------");
        }
    }

    public static void main(String[] args) {
        System.out.println("=================================================");
        System.out.println("☁️ ENTERPRISE CLOUD DATABASE POOL CONFIG MANAGER");
        System.out.println("=================================================
");

        // Profile 1: Using No-arg Chained Constructor
        ConnectionPoolConfig devConfig = new ConnectionPoolConfig();
        devConfig.printAuditReport();

        // Profile 2: Using Production Master Constructor
        ConnectionPoolConfig prodConfig = new ConnectionPoolConfig(
            "AwsAuroraPrimaryPool",
            "jdbc:postgresql://aurora-cluster.us-east-1.rds.amazonaws.com:5432/finance_prod",
            20, 100, 10000, true
        );
        prodConfig.printAuditReport();

        // Profile 3: Using Copy Constructor for Failover Replica
        ConnectionPoolConfig replicaConfig = new ConnectionPoolConfig(prodConfig);
        replicaConfig.printAuditReport();

        System.out.println("=================================================");
        System.out.println("🎉 PART 03 (ARRAYS, METHODS & OOP) COMPLETED 100%!");
        System.out.println("=================================================");
    }
}