K&B SelfTest Ques ,chap 9 pg 739

[Lucky J Verma]

Hi,

I have some doubt regarding answers mentioned to Question 12 in Self test exam chap 9,page 738-739.
Ques says ,how to make this application thread safe.

anser book says : is making methods synchronized.

but what i think aswer should be :
making methods synchronzied
and se stringBffer instead of StringBuilder.
As there can be more than 1 answers.
althouht ,we cannt rely n thread-safe classes but it also helps.


So for SCJP, how we get to knw ,as both are right ansers.or for sure ,they put no of possible ansers.

[christian combarel]

Hello,
Just replacing StringBuilder by StringBuffer doesn't make class Logger thread-safe : if multiple threads call concurrently the method log, the data into contents could be (will be !) corrupted. Read again the "Thread-Safe Classes" section from the K&B p714.
If the log method is synchronized, it's make the class thread-safe and using the thread-safe class StringBuffer is useless.

[sandeep atluri]

hi there...

you asked... why mark the method as synchronized when we can use stringBuffer to make thread safe code.....???

Answer:

When we mark the method as synchronized, what happens is,the method is called atmost by one Object/thread at a time and until this thread is done using this particular method, no other thread can enter and use this method... kind of a queue....

in StringBuffer class all the methods are individually marked as synchronized....
now lets imagine a scenario when there are two threads executing simultaneously... each on different methods, but come to a point where they need a method to complete their execution.. creating a deadlock.....

"thread-safe" class will fail....

NOTE:
just because a class is described as "thread-safe, doesn't meant that it is always thread-safe"

.

besides why rely on classes when you can get away by just marking a single method as Synchronized....

if you want more ...read chapter 9: page 714 K&B..carefully...

good luck,.........