class Program {
    public static final int TOTAL_ITERATIONS = 1000000;

    private static final int NUM_ACCOUNTS = 2;

    public static void main(String[] args) {
        Bank bank = new Bank(NUM_ACCOUNTS);

        Thread accountTransfer1 = new Thread(new AccountTransferRunnable(bank));
        Thread accountTransfer2 = new Thread(new AccountTransferRunnable(bank));

        accountTransfer1.start();
        accountTransfer2.start();

        try {
            accountTransfer1.join();
            accountTransfer2.join();
        } catch (InterruptedException ex) {
            //
        }
    }
}

public class Account {
    private int mBalance;

    public Account() {
        mBalance = 0;
    }

    public int getBalance() {
        return mBalance;
    }

    public void withdraw(int value) {
        mBalance -= value;
    }

    public void deposit(int value) {
        mBalance += value;
    }
}

public class Bank {
    private List<Account> mAccounts;
    private int mSlots;

    public Bank(int slots) {
        mAccounts = new ArrayList<Account>(Collections.nCopies(slots, new Account()));
        mSlots = slots;
    }

    public int getSlots() {
        return mSlots;
    }

    public int getBalance(int id) {
        Account account = mAccounts.get(id);

        synchronized(account) {
            return account.getBalance();
        }
    }

    public void withdraw(int id, int value) {
        Account account = mAccounts.get(id);

        synchronized(account) {
            account.withdraw(value);
        }
    }

    public void deposit(int id, int value) {
        Account account = mAccounts.get(id);

        synchronized(account) {
            account.deposit(value);
        }
    }

    public void transfer(int fromId, int toId, int value) {
        Account fromAccount = mAccounts.get(fromId);
        Account toAccount = mAccounts.get(toId);

        synchronized(fromAccount) {
            synchronized(toAccount) {
                fromAccount.withdraw(value);
                toAccount.deposit(value);
            }
        }
    }

}

public class AccountTransferRunnable implements Runnable {
    private final Bank mBank;

    public AccountTransferRunnable(Bank bank) {
        mBank = bank;
    }

    @Override
    public void run() {
    Random random = new Random();

    int slots = mBank.getSlots();
        int fromId, toId;

        for(int i = 0; i < Program.TOTAL_ITERATIONS; i++) {
            fromId = random.nextInt(slots);

            do {
                toId = random.nextInt(slots);
            } while(toId == fromId);

            mBank.transfer(fromId, toId, 100);
        }
   }
}