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Multi Thread Question

 
Roger Zhao
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Hi, all:
Given:
1. public class SyncTest {
2. private int x;
3. private int y;
4. private synchronized void setX( int i ) { x = i; }
5. private synchronized void setY( int i ) { y = i; }
6. public void setXY( int i ) { setX(i); setY(i); }
7. public synchronized boolean check() { return x != y; }
8. }
Under which condition will check return true when called from a different class?
A. check can never return true.
B. check can return true when setXY is called by multiple threads.
C. check can return true when multiple threads call setX and setY separately.
D. check can return true only if SyncTest is changed to allow x and y to be set separately.
I choose B. Right? Check,SetX,SetY are synchronized methods and x,y are private vars, but SetXY is normal method. The value of x,y can be set different when multi-thread calls SetXY.
Anybody give me a full explanation about it?

Thanks a lot,
Roger
 
Ernest Friedman-Hill
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B is probably the closest answer, but this is a badly worded question. The right answer is the non-existent E, "check can return true when setXY() and check() are called from different threads, nearly simultaneously."
 
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