Solution: The Joint Bank Account

public class JointBankAccount {
    static class BankAccount {
        private String accountId;
        private int balance;
        public BankAccount(String accountId, int balance) {
            this.accountId = accountId;
            this.balance = balance;
        }
        // 1. synchronized protects this specific account instance
        public synchronized void withdraw(int amount) {
            String name = Thread.currentThread().getName();
            
            // 2. Log the attempt with the Account ID
            System.out.println("[" + accountId + "] " + name + " is requesting $" + amount + "...");
            if (balance >= amount) {
                System.out.println("[" + accountId + "] " + name + " is verifying balance...");
                
                try {
                    Thread.sleep(100); // Simulate processing time
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                // 3. Safe modification
                balance -= amount;
                System.out.println("[" + accountId + "] Transaction Approved for " + name + ". Remaining: $" + balance);
            } else {
                System.out.println("[" + accountId + "] Transaction Denied for " + name + ". Insufficient funds.");
            }
        }
    }
    public static void main(String[] args) {
        // 4. The shared resource
        BankAccount sharedAccount = new BankAccount("SAV-2026-0112", 100);
        // 5. Define the withdrawal task with random delay
        Runnable withdrawalTask = () -> {
            // Random delay (0-50ms) to ensure fair chance for both threads
            try { Thread.sleep((long) (Math.random() * 50)); } catch (InterruptedException e) { }
            sharedAccount.withdraw(80);
        };
        // 6. Create threads sharing the same task
        Thread alice = new Thread(withdrawalTask, "Alice");
        Thread bob = new Thread(withdrawalTask, "Bob");
        // 7. Start threads
        alice.start();
        bob.start();
        try {
            // 8. Wait for completion
            alice.join();
            bob.join();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        
        System.out.println("Final Account Balance: $" + sharedAccount.balance);
    }
}