• Post Reply Bookmark Topic Watch Topic
  • New Topic
programming forums Java Mobile Certification Databases Caching Books Engineering Micro Controllers OS Languages Paradigms IDEs Build Tools Frameworks Application Servers Open Source This Site Careers Other all forums
this forum made possible by our volunteer staff, including ...
  • Campbell Ritchie
  • Paul Clapham
  • Ron McLeod
  • Liutauras Vilda
  • Bear Bibeault
  • Jeanne Boyarsky
  • Tim Cooke
  • Devaka Cooray
Saloon Keepers:
  • Tim Moores
  • Tim Holloway
  • Piet Souris
  • salvin francis
  • Stephan van Hulst
  • Frits Walraven
  • Carey Brown
  • Jj Roberts

Thread question

Posts: 28
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
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() {
public synchronized void b() {
i.inc(); j.inc(); k.inc();
i.dec(); j.dec(); k.dec();
public void c() {
The correct answers are:
i.v is always guaranteed to be 0 or 1.
j.v is guaranteed always to be 0 or 1.
Can anyone explain how?
Posts: 23
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
sorry couldnt understand the ques. if any part of q is left out or any part of code is left out pls post that also. also give all the ans options if you have.
Ranch Hand
Posts: 76
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
G: The question is as complete as it can be...
Sarah: Would you be so kind to use the UBB-"code"-tag?! The code is much easier to read that way...
Now to the answer:
a() and b() are declared synchronized, that means that any thread calling these methods has to wait for a possible other thread just working on them (no thread is working on a() while another do, the same holds for b()). So if you refer to i.v, it may be 0 ("most time"), but if a thread just had increased but not (yet) decreased i (via calling a()), it may be 1. Analogous about j.v.
This does not hold for k.v, b/c c() is /not/ declared synchronized. So 1000 or more threads may call c() at the same time, all increasing k; if you refer to k.v before these threads have decreased k again, then k.v may be 1000 (or more).
Hope it helps
Ranch Hand
Posts: 3141
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
g krishnan
Please read the JavaRanch Name Policy and re-register using a name that complies with the rules.
Thanks for your cooperation.
Jane Griscti
Sun Certified Programmer for the Java� 2 Platform
Well don't expect me to do the dishes! This ad has been cleaned for your convenience:
Thread Boost feature
    Bookmark Topic Watch Topic
  • New Topic