为什么我必须同步线程的ArrayList？

Question

So i need to create an ArrayList of Threads but according to

Java - Filling an ArrayList of Threads with loop

it seems that i need to use the synchronized keyword, my question then is:

If im calling this only on the main thread why do i have to use the synchronized keyword? There are no others threads that could potentially do the same right?

ArrayList<Thread> t = new ArrayList<Thread>();
for(int i=0;i<love.size();i++){
    BTConnection cbtc = love.get(i).btc;
    if(cbtc!=null){
        Communicate temp = new Communicate(cbtc);
        Thread ttemp = new Thread(temp);
        ttemp.start();
        t.add(ttemp);   
    }
}

Moreover if right below the code i use:

for(int i=0;i<t.size();i++){
    t.get(i).join();
}

Does the for loop stop until the ith thread returns and then proceed to wait for the ith+1?

Answer 1

I don't see any reason why you would need to synchronize the threadlist, if only one thread is adding values into it/reading from it. As for the second part, you are correct, the join -call will block until the i 'th thread has finished, before moving to wait for the next one.