code: private void readObject(ObjectInputStream stream)
           throws IOException, ClassNotFoundException
      {
          stream.defaultReadObject();
          if (serialVersionOnStream < 1) {
              // Didn't have capitalizationSetting, set it to default
              capitalizationSetting = DisplayContext.CAPITALIZATION_NONE;
          }
  
          // if deserialized from a release that didn't have booleanAttributes, add them all
          if(booleanAttributes == null) {
              booleanAttributes = EnumSet.allOf(BooleanAttribute.class);
          }
  
          serialVersionOnStream = currentSerialVersion;
      }
docs: First, read in the default serializable data.
  
  Then, if <code>serialVersionOnStream</code> is less than 1, indicating that
  the stream was written by a pre-ICU-53 version,
  set capitalizationSetting to a default value.
  Finally, set serialVersionOnStream back to the maximum allowed value so that
  default serialization will work properly if this object is streamed out again.