Say I have two threads and an object. One thread assigns the object:

public void assign(MyObject o) {
    myObject = o;
}

Another thread uses the object:

public void use() {
    myObject.use();
}

Does the variable myObject have to be declared as volatile? I am trying to understand when to use volatile and when not, and this is puzzling me. Is it possible that the second thread keeps a reference to an old object in its local memory cache? If not, why not?

Thanks a lot.