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Troubleshooting and fixing deadlock

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I came across this question recently where I am suppose to find the deadlock in the code present below. I have no experience with Java or multithreading, that's why I am here to understand the problem better.

public class BankAccount {
  private final int customerId;
  private int balance;

  public BankAccount(int customerId, int openingBalance) {
    this.customerId = customerId;
    this.balance = openingBalance;

  public void withdraw(int amount) throws OverdrawnException {
    if (amount > balance) {
      throw new OverdrawnException();
    balance -= amount;

  public void deposit(int amount) {
    balance += amount;

  public int getCustomerId() {
    return customerId;

  public int getBalance() {
    return balance;

class TransferOperation extends Thread {
    int threadNum;

    TransferOperation(int threadNum) {
        this.threadNum = threadNum;

    private void transfer(BankAccount fromAccount, BankAccount toAccount, int transferAmount) throws OverdrawnException {
        synchronized (fromAccount) {                    
            synchronized (toAccount) {

    // ...

I have this above piece of code. I want to find where a deadlock could occur in the above code. I think only place it could occur is in the two synchronized blocks. Am I right?

If yes, can someone help me understand why? I can guess that it is probably because withdraw and deposit keeps one thread waiting for another. But this is a total guess, that's why asking for help here.

Also if I would want to prevent the deadlock, how would I go about it in the code?

Any help appreciated.

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