Synchronization

[Padma Priya]

hi Everyone

I am new to threads and having a problem understanding the concept of Synchronization.

I am providing the code below:

Given:

public class Letters extends Thread {
private String name;
public Letters(String name) {
this.name = name;
}

public void write () {
System.out.print(name);
System.out.print(name);
}
public static void main(String[] args) {
new Letters("X").start();
new Letters("Y").start();
}
}

We want to guarantee that the output can be either XXYY or YYXX, but never XYXY or any other combination. Which of the following method definitions could be added to the Letters class to make this guarantee? (Choose all that apply.)

A)public void run() { write(); }

B)public synchronized void run() { write(); }

C)public static synchronized void run() { write(); }

D)public void run() { synchronized(this) { write(); } }

E)public void run() { synchronized(Letters.class) { write(); } }

F)public void run () { synchronized (System.out) { write (); } }

G)public void run() { synchronized(System.out.class) { write(); } }

The correct answers for this question are E and F.
But i was wondering why option B also cannot be the right answer for this question.

Can anybody explain...

Thanks in advance

With regards
Deepthi

[Peter Chase]

Because (B) synchronises on the instance of Thread. The two threads have different instances of Thread, so the synchronisation does not prevent them running simultaneously.

[Nitesh Kant]

Option B is not correct because that will hold an instance level lock and since both the threads are different instances, none of them will wait for the other.