Assume two threads share a BankAccount object with balance of zero (0), and that the BankAccount class provides deposit and withdraw methods and has a ReentrantLock named myLock, as shown below. Note that only the deposit method uses the lock. Thread one deposits $10 ten times and, concurrently, thread two withdraws $10 ten times. Which statement regarding the balance after all thread calls is definitely true?
Public void deposit(int dollars)
{
MyLock.lock()
Int newBalance = balance + dollars;
System.out.println("depositing");
Balance = newBalance;
MyLock.unlock()
}
Public void withdraw(int dollars)
{
Int newBalance = balance - dollars;
System.out.println("withdrawing");
Balance = newBalance;
}
A) The balance could be zero or positive.
B) The balance is zero.
C) The balance could be zero or negative.
D) The balance is positive.

Question

Quizplus · Accepted Answer

Since the BankAccount object starts with a balance of zero, there is a possibility that thread two withdraws all the money before thread one has finished depositing. This means that the final balance could end up being negative. However, it is also possible that all ten deposits by thread one are completed before any withdrawals by thread two, resulting in a final balance of zero. Therefore, the balance could be zero or negative, but it cannot be positive.

Assume Two Threads Share a BankAccount Object with Balance of Zero