fomr javaoc of ReentrantReadWriteLock
an example:
class CachedData {
  Object data;
  volatile boolean cacheValid;
  ReentrantReadWriteLock rwl = new ReentrantReadWriteLock();

  void processCachedData() {
    rwl.readLock().lock();
    if (!cacheValid) {
     .....
    use(data);
    rwl.readLock().unlock();
  }
}
Using volatile here makes sense to me.

but if in my class looks like this,
class CachedData {
  HashMap<Key, Obj> data; // <---- here
  ReentrantReadWriteLock rwl = new ReentrantReadWriteLock();

  void processCachedData(Key k) {
    rwl.readLock().lock();
    if (!data.containsKey(k)) {  // <--- here
     .....
    use(data);
    rwl.readLock().unlock();
  }
}

should I declare as
"volatile HashMap"

or for which "variable" type should I apply volatile in such
situation?

thanks.