Need help about Thread issue

Question

Given from scjp
1.public static void main(String[] args) {
2.        NameRunnable nr = new NameRunnable();
3.        Thread t1 = new Thread(nr);              
4.        t1.start();
5.        t1.join();                   
}There are some questions which i made up myself to test how i understand about the thread issue and I really need some experts to confirm about it.
Question 1: At line 3, how many threads we have now ?
my answer is
there are 2 threads. the first one is main thread and the second one is t.
I am not sure about the t thread because in the book, they indicate that after instantiating the thread,
we just have a thread object but not a true thread.
Question 2: At line 4, after t1.start(), which thread will be executed first.
My answer is
we dont know because it depends on the scheduler.
Question 3: what t1.join() does ?
my answer is
blablabla.What I am thinking is t.join() joins the current thread to the end of t so that when t finishes the current thread can run again. However, which one is the current thread now. That is why I am stuck
Please help me. I appreciate
Edited by: newbie on Nov 25, 2010 4:46 PM
Edited by: newbie on Nov 25, 2010 4:47 PM
Edited by: newbie on Nov 25, 2010 4:49 PM

Answer 1

newbie wrote:
Given from scjp
public static void main(String[] args) {
NameRunnable nr = new NameRunnable();
Thread t1 = new Thread(nr);              
t1.start();
t1.join();                   
}There are some questions which i made up myself to test how i understand about the thread issue and I really need some experts to confirm about it.
Question 1: At line 3, how many threads we have now ?
my answer is
there are 2 threads. the first one is main thread and the second one is t.
I am not sure about the t thread because in the book, they indicate that after instantiating the thread,
we just have a thread object but not a true thread.
Don't use code blocks for prose. It won't autowrap and can lead to display problems if a line is too long.
Which is line 3?
What do you mean by "how many threads to we have?" Do you mean how many Thread objects exist, or how many threads (lower case "t") are executing.
After you have called t1.start(), there are at least 2 threads executing--the main thread, and the one you started. I say "at least" because the JVM has some administrative threads of its own.
Question 2: At line 4, after t1.start(), which thread will be execute first.
My answer is
we dont know because it depends on the scheduler.
Correct. And don't think of one executing "first." They can take turns, or they can both execute at the same time (if you have a multicore or multi-CPU machine).
Question 3: what t1.join() does ?
my answer is
blablabla.What I am thinking is t.join() joins the current thread to the end of t so that when t finishes the current thread can run again. However, which one is the current thread now. That is why I am stuck
Please help me. I appreciateDid you read [url http://download.oracle.com/javase/6/docs/api/java/lang/Thread.html#join()]the docs for join()? They tell you exactly what it does. If you don't understand after reading, post again.