Java How to Program (early objects), 9/e

17.5 Object Serialization

In Section 17.4, we demonstrated how to write the individual fields of an AccountRecord object into a file as text, and how to read those fields from a file and place their values into an AccountRecord object in memory. In the examples, AccountRecord was used to aggregate the information for one record. When the instance variables for an AccountRecord were output to a disk file, certain information was lost, such as the type of each value. For instance, if the value "3" is read from a file, there’s no way to tell whether it came from an int, a String or a double. We have only data, not type information, on a disk. If the program that’s going to read this data “knows” what object type the data corresponds to, then ...