Is java.util.Calendar thread safe or not?

Question

I\'ve been working under the assumption that neither Date nor Calendar are thread-safe, but, during a recent discussion, a co-worker told me

Answer 1

Documentation from Oracle says nothing about thread-safety: http://docs.oracle.com/javase/7/docs/api/java/util/Calendar.html.

OpenJDK source code (build b147) implements java.util.Calendar in a non-thread-safe way, for example:

public void setTimeInMillis(long millis) {
  // skipped
  time = millis;
  isTimeSet = true;
  areFieldsSet = false;
  computeFields();
  areAllFieldsSet = areFieldsSet = true;
}

I think that it's safe to assume that the class is not thread safe.