Thread Question

[Mike Cutter]

I saw this question in a mock exam. Can anyone explain how to arrive at the answer?

public class Test {
private int a;
private int b;
private synchronized void A(int c) {a=c;}
private synchronized void B(int c) {b=c;}
public void AB(int c) {A(c); B(c);}
public synchronized boolean d() {return a != b;}
}
Under which condition will d return true when called from a different class?
A. d can never return true when multiple threads call A and B separately
B. d can never return true only if Test is changed to allow a and b to be set separately
C. d can never return true when AB is called by multiple threads
D. d can never return true

[Jessica Sant]

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[Paul Villangca]

Weird question. It asks when d will return true, yet the options state when d never returns true.
A. d can never return true when multiple threads call A and B separately
It can still return true when the AB() and d() methods are running at the same time (?)

B. d can never return true only if Test is changed to allow a and b to be set separately
Huh? In fact, there's a greater likelihood of d returning true if Test is changed this way!

C. d can never return true when AB is called by multiple threads
D. d can never return true
refer to (A.)