question: private void readObject ( ObjectInputStream s ) throws IOException , ClassNotFoundException { s . defaultReadObject ( ) ; }
target:  Adds semantic checks to the default deserialization method. This method must have the standard signature for a readObject method, and the body of the method must begin with "s.defaultReadObject();". Other than that, any semantic checks can be specified and do not need to stay the same from version to version. A readObject method of this form may be added to any class, even if Tetrad sessions were previously saved out using a version of the class that didn't include it. (That's what the "s.defaultReadObject();" is for. See J. Bloch, Effective Java, for help.