join() vs. synchronized

[Kee Kee moon]

Below program is from Cathy and Bert.

It will produce the same result, account will not be overdrawn, by using either join() or synchronized. Which one is better, join() or synchronized and why.
Thank you very much in advance.

class Account {
	private int balance = 50;
	public int getBalance() {
		return balance;
	}
	public void withdraw(int amount) {
			balance = balance - amount;
	}
}

public class AccountDanger implements Runnable {
	private Account acct = new Account();
	public static void main (String [] args) throws InterruptedException {
		AccountDanger r = new AccountDanger();
		Thread one = new Thread(r);
		Thread two = new Thread(r);
		one.setName("Fred");
		two.setName("Lucy");
		one.start();
		two.start();
		two.join();                     // join() 
	}
	public void run() {
		for (int x = 0; x < 5; x++) {
			makeWithdrawal(10);
			if (acct.getBalance() < 0) {
				System.out.println("account is overdrawn! ");
			}
		}
	}
	private synchronized void makeWithdrawal(int amt) {    // by using synchronized
		if (acct.getBalance() >= amt) {
			System.out.println(Thread.currentThread().getName() +
					" is going to withdraw");
			try {
				Thread.sleep(500);
			} catch(InterruptedException ex) { }
			acct.withdraw(amt);
			System.out.println(Thread.currentThread().getName() +
					" completes the withdrawal");
		} else {
			System.out.println("Not enough in account for " +
					Thread.currentThread().getName() + " to withdraw " +
					acct.getBalance());
		}
	}
}

[Henry Wong]

Kee Kee moon wrote:
It will produce the same result, account will not be overdrawn, by using either join() or synchronized. Which one is better, join() or synchronized and why.
Thank you very much in advance.

These are two differnt mechanism, that are only somewhat related. Synchronization is a locking mechanism that allows to threads to not step on each other. The join() method call allows one thread to wait for the completion of another thread. In fact, the join() method actually uses synchronization under the covers.

Henry

[Kee Kee moon]

Henry Wong wrote:

Kee Kee moon wrote:
It will produce the same result, account will not be overdrawn, by using either join() or synchronized. Which one is better, join() or synchronized and why.
Thank you very much in advance.

These are two differnt mechanism, that are only somewhat related. Synchronization is a locking mechanism that allows to threads to not step on each other. The join() method call allows one thread to wait for the completion of another thread. In fact, the join() method actually uses synchronization under the covers.

Henry

What if I use both, join() and synchronized, any negative impact of using both? The result will be the same if I use both.
Thanks

[Ankit Garg]

Kee Kee moon wrote:What if I use both, join() and synchronized, any negative impact of using both? The result will be the same if I use both.

The example code that you have shown here actually doesn't use the join method to provide thread safety. So if you remove synchronization, the account might be overdrawn. Generally synchronization is used to achieve thread safety...

[Kee Kee moon]

Ankit Garg wrote:

Kee Kee moon wrote:What if I use both, join() and synchronized, any negative impact of using both? The result will be the same if I use both.

The example code that you have shown here actually doesn't use the join method to provide thread safety. So if you remove synchronization, the account might be overdrawn. Generally synchronization is used to achieve thread safety...

I got it, thank you very much for the clarification.