java-question

answer.java

// ============================================
// 1. PAYMENT METHOD STRATEGIES (Strategy Pattern)
// ============================================

// Payment Strategy Interface
interface PaymentStrategy {
    void processPayment(double amount, String transactionType);
}

// Concrete Payment Strategies
class CashPayment implements PaymentStrategy {
    @Override
    public void processPayment(double amount, String transactionType) {
        System.out.println(transactionType + " of ₹" + amount + " via Cash (Physical Submission)");
    }
}

class RTGSPayment implements PaymentStrategy {
    @Override
    public void processPayment(double amount, String transactionType) {
        System.out.println(transactionType + " of ₹" + amount + " via RTGS");
    }
}

class OnlinePayment implements PaymentStrategy {
    @Override
    public void processPayment(double amount, String transactionType) {
        System.out.println(transactionType + " of ₹" + amount + " via Online Banking");
    }
}

class GooglePayPayment implements PaymentStrategy {
    @Override
    public void processPayment(double amount, String transactionType) {
        System.out.println(transactionType + " of ₹" + amount + " via Google Pay");
    }
}

// ============================================
// 2. PAYMENT STRATEGY FACTORY (Factory Pattern)
// ============================================

class PaymentStrategyFactory {
    private PaymentStrategyFactory() {} // Singleton-like behavior
    
    public static PaymentStrategy createDepositStrategy(String method) {
        switch (method.toUpperCase()) {
            case "CASH": return new CashPayment();
            case "RTGS": return new RTGSPayment();
            case "ONLINE": return new OnlinePayment();
            case "GOOGLEPAY": return new GooglePayPayment();
            default: throw new IllegalArgumentException("Invalid deposit method: " + method);
        }
    }
    
    public static PaymentStrategy createWithdrawStrategy(String method) {
        switch (method.toUpperCase()) {
            case "ONLINE": return new OnlinePayment();
            case "GOOGLEPAY": return new GooglePayPayment();
            default: throw new IllegalArgumentException("Invalid withdrawal method: " + method);
        }
    }
}

// ============================================
// 3. ACCOUNT STATE INTERFACE (State Pattern)
// ============================================

interface AccountState {
    void deposit(double amount, PaymentStrategy strategy);
    void withdraw(double amount, PaymentStrategy strategy);
    String getStateName();
}

// ============================================
// 4. CONCRETE STATES (State Pattern + Null Object Pattern)
// ============================================

class OpenedState implements AccountState {
    @Override
    public void deposit(double amount, PaymentStrategy strategy) {
        if (amount <= 0) {
            System.out.println("Invalid amount for deposit");
            return;
        }
        System.out.println("[OPENED ACCOUNT - DEPOSIT]");
        strategy.processPayment(amount, "Deposit");
        System.out.println("Deposit successful!\n");
    }
    
    @Override
    public void withdraw(double amount, PaymentStrategy strategy) {
        if (amount <= 0) {
            System.out.println("Invalid amount for withdrawal");
            return;
        }
        System.out.println("[OPENED ACCOUNT - WITHDRAWAL]");
        strategy.processPayment(amount, "Withdrawal");
        System.out.println("Withdrawal successful!\n");
    }
    
    @Override
    public String getStateName() {
        return "OPENED";
    }
}

class ClosedState implements AccountState {
    @Override
    public void deposit(double amount, PaymentStrategy strategy) {
        System.out.println("[CLOSED ACCOUNT]");
        System.out.println("❌ Deposit operation not available - Account is closed\n");
    }
    
    @Override
    public void withdraw(double amount, PaymentStrategy strategy) {
        System.out.println("[CLOSED ACCOUNT]");
        System.out.println("❌ Withdrawal operation not available - Account is closed\n");
    }
    
    @Override
    public String getStateName() {
        return "CLOSED";
    }
}

// ============================================
// 5. ACCOUNT TYPE ABSTRACTION
// ============================================

abstract class BankAccount {
    protected String accountNumber;
    protected AccountState state;
    protected double balance;
    
    public BankAccount(String accountNumber) {
        this.accountNumber = accountNumber;
        this.state = new OpenedState(); // Default state
        this.balance = 0.0;
    }
    
    public void setState(AccountState state) {
        this.state = state;
        System.out.println("Account state changed to: " + state.getStateName());
    }
    
    public void deposit(double amount, String paymentMethod) {
        PaymentStrategy strategy = PaymentStrategyFactory.createDepositStrategy(paymentMethod);
        state.deposit(amount, strategy);
        if (state instanceof OpenedState) {
            balance += amount;
        }
    }
    
    public void withdraw(double amount, String paymentMethod) {
        PaymentStrategy strategy = PaymentStrategyFactory.createWithdrawStrategy(paymentMethod);
        state.withdraw(amount, strategy);
        if (state instanceof OpenedState && balance >= amount) {
            balance -= amount;
        }
    }
    
    public abstract void displayAccountType();
    
    public double getBalance() {
        return balance;
    }
}

// ============================================
// 6. CONCRETE ACCOUNT TYPES
// ============================================

class SavingsAccount extends BankAccount {
    public SavingsAccount(String accountNumber) {
        super(accountNumber);
    }
    
    @Override
    public void displayAccountType() {
        System.out.println("Account Type: SAVINGS");
        System.out.println("Account Number: " + accountNumber);
        System.out.println("Current Balance: ₹" + balance);
        System.out.println("State: " + state.getStateName());
    }
}

class CurrentAccount extends BankAccount {
    public CurrentAccount(String accountNumber) {
        super(accountNumber);
    }
    
    @Override
    public void displayAccountType() {
        System.out.println("Account Type: CURRENT");
        System.out.println("Account Number: " + accountNumber);
        System.out.println("Current Balance: ₹" + balance);
        System.out.println("State: " + state.getStateName());
    }
}

// ============================================
// 7. ACCOUNT FACTORY (Factory Pattern)
// ============================================

class BankAccountFactory {
    public static BankAccount createAccount(String type, String accountNumber) {
        switch (type.toUpperCase()) {
            case "SAVINGS": 
                return new SavingsAccount(accountNumber);
            case "CURRENT": 
                return new CurrentAccount(accountNumber);
            default: 
                throw new IllegalArgumentException("Invalid account type: " + type);
        }
    }
}

// ============================================
// 8. MAIN CLASS - DEMONSTRATION
// ============================================

public class BankingSystemDemo {
    public static void main(String[] args) {
        System.out.println("========== BANKING SYSTEM DEMO ==========\n");
        
        // Create a Savings Account using Factory
        BankAccount savingsAccount = BankAccountFactory.createAccount("SAVINGS", "SAV123456");
        savingsAccount.displayAccountType();
        System.out.println();
        
        // Deposit operations with different payment methods (Opened State)
        System.out.println("--- DEPOSIT OPERATIONS ---");
        savingsAccount.deposit(5000, "CASH");
        savingsAccount.deposit(3000, "RTGS");
        savingsAccount.deposit(2000, "ONLINE");
        savingsAccount.deposit(1000, "GOOGLEPAY");
        
        // Withdraw operations with different payment methods
        System.out.println("--- WITHDRAWAL OPERATIONS ---");
        savingsAccount.withdraw(1500, "ONLINE");
        savingsAccount.withdraw(500, "GOOGLEPAY");
        
        System.out.println("Current Balance: ₹" + savingsAccount.getBalance());
        System.out.println();
        
        // Close the account
        System.out.println("--- CLOSING ACCOUNT ---");
        savingsAccount.setState(new ClosedState());
        System.out.println();
        
        // Try operations on closed account
        System.out.println("--- ATTEMPTING OPERATIONS ON CLOSED ACCOUNT ---");
        savingsAccount.deposit(1000, "CASH");
        savingsAccount.withdraw(500, "ONLINE");
        
        // Reopen account
        System.out.println("--- REOPENING ACCOUNT ---");
        savingsAccount.setState(new OpenedState());
        savingsAccount.deposit(2000, "ONLINE");
        
        System.out.println("\nFinal Balance: ₹" + savingsAccount.getBalance());
    }
}