Why is volatile keyword not allowed for local variables?

Question

Consider the snippet:

If in a main thread, I have this inside a method-

volatile CountDownLatch latch = new CountDownLatch(3);

new Thread(new ProcessThread("Worker1",latch, 20000)).start();//20 secs
new Thread(new ProcessThread("Worker2",latch, 60000)).start();//60 secs
new Thread(new ProcessThread("Worker3",latch, 40000)).start();//40 secs

I see that volatile is shown as an illegal modifier. And only final is permitted. And final guarantees initialization safety.

public static class ProcessThread implements Runnable {
  final CountDownLatch latch;
  final long workDuration;
  final String name;

  public ProcessThread(String name, CountDownLatch latch, long duration){
      this.name= name;
      this.latch = latch;
      this.workDuration = duration;
  }
}

The object below i.e new CountDownLatch(3) is properly constructed but I also want to make sure that the reference latch to which the above object is assigned is guaranteed to be visible to the code below it.

final CountDownLatch latch = new CountDownLatch(3);

Does the above code guarantee initialization so that latch is perfectly visible to the code below i.e

new Thread(new ProcessThread("Worker1",latch, 20000)).start();

Answer 1

Local variables live on the stack; and of course, when you invoke the same method twice, they have all their local variables on their individual stacks.

volatile only makes sense when multiple threads would be writing to the same memory location (on the heap).

Which makes absolutely no sense for local variables from within the body of a method!