threads

[preeti khane]

  
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(); 
} 
} 
1) i.v is guaranteed always to be 0 or 1. 
2) j.v is guaranteed always to be 0 or 1. 
3) k.v is guaranteed always to be 0 or 1 
4) j.v will always be greater than or equal to k.v at any give time. 
5) k.v will always be greater than or equal to j.v at any give time. 

Can someone give me the correct answers and explanation
thank you

[Reshma Shanbhag]

i guess the answers are 1, 2 and 3.
The methods a(), b() and c() are synchronized. So any thread that is accessing one of the methods cannot access rest two untill it finishes with the first method in a given object of class Q7ed5. Every method takes care of incrementing as well as decrementing the variables too, hence the value of variable 'v' switches between 0 and 1.
If am wrong correct me.
[ April 03, 2003: Message edited by: Reshma Pai ]
[ April 03, 2003: Message edited by: Reshma Pai ]

[preeti khane]

Answer in the exam is only 1 and 2

[Reshma Shanbhag]

Hey i mistaked thinking that method c() is synchronized.. since it is not, thevalue of k.v cannot be predcited...
the Answer's 1 & 2 are right.. sorry for the mistake .
reshma
[ April 03, 2003: Message edited by: Reshma Pai ]