How do objects behave in multithreaded classes?

Question

Java

If a class A that extends Thread creates an object of a class that is not multi-threaded then the instruction of that class will be executed on the main thread or on the thread created by class A ?
class Main {
public static void main(args)
{
new A.start();
}
}
class A extends Thread {
public void run(){
OtherClass otherClass = new OtherClass()
}
}
class OtherClass {
//code in this thread will be
//executed in the thread created by class A
//or in the main thread ?
}

Answer 1

in stream A.

Answer 2

I recommend a very simple and visual article about threads:
skipy.ru/technics/synchronization.html