code: public boolean changePriority(E key, double priority) {
      Entry<E> entry = getEntry(key);
      if (entry == null) {
        entry = makeEntry(key);
      }
      if (compare(priority, entry.priority) == 0) {
        return false;
      }
      entry.priority = priority;
      heapify(entry);
      return true;
    }
docs: Changes a priority, either up or down, adding the key it if it wasn't there already.
  
  @param key an <code>Object</code> value
  @return whether the priority actually changed.