Thread Confinement

Question

I am reading Java Concurrency in Practice and kind of confused with the thread confinement concept. The book says that

When an object is confined to a

Answer 1

That's exactly what it means. The object itself is accessed by only one thread, and is thus thread-safe. ThreadLocal objects are a kind of objects that are bound to an only thread

Answer 2

I guess that's what want to say. Like creating a object inside the run method and not passing the reference to any other instance.

Simple example:

public String s;

public void run() {
  StringBuilder sb = new StringBuilder();
  sb.append("Hello ").append("world");
  s = sb.toString();
}

The StringBuilder instance is thread-safe because it is confined to the thread (that executes this run method)