Dumb question about threads

[Max Bazhenov]

Given the following code, which statements concerning the objects referenced through the member variables i, j and k are true, given that any thread may call the methods a(), b() and c() at any time?

 
class Counter {
    int v = 0;
    synchronized void inc() { v++; }
    synchronized void dec() { v--; }
}
public class Q7ed5 {
    Counter i;
    Counter j;
    Counter k;
    public synchronized void a() {
        i.inc();
        System.out.println("a");
        i.dec();
    }
    public synchronized void b() {
        i.inc(); j.inc(); k.inc();
        System.out.println("b");
        i.dec(); j.dec(); k.dec();
    }
    public void c() {
        k.inc();
        System.out.println("c");
        k.dec();
    }
}

A. i.v is guaranteed always to be 0 or 1.
B. j.v is guaranteed always to be 0 or 1.
C. k.v is guaranteed always to be 0 or 1.
D. j.v will always be greater than or equal to k.v at any give time.
E. k.v will always be greater than or equal to j.v at any give time.

ANSWERS: A, B
Why A is correct? Assume that one thread executes method's a() i.inc(), after that another thread executes method's b() i.inc().
Value of i.v will be 2, isn't it ?
Where am I mistaken ?
[ November 12, 2004: Message edited by: Barry Gaunt ]

[Barry Gaunt]

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