Files, Streams and Object Serialization - Java: How to Program Early Objects - page 670

Account First Name Last Name Balance
100 Bob Blue 24.98
200 Steve Green -345.67
300 Pam White 0.00
400 Sam Red -42.16
500 Sue Yellow 224.62
No more records
Fig. 15.11 | Reading a file of objects sequentially with ObjectInputStream and displaying
each record. (Part 3 of 3.)
The program reads records from the file in method readRecords (lines 37-66). Line
46 calls ObjectInputStream method readObject to read an Object from the file. To use
Account -specific methods, we downcast the returned Object to type Account . Method
readObject throws an EOFException (processed at lines 54-57) if an attempt is made to
read beyond the end of the file. Method readObject throws a ClassNotFoundException
if the class for the object being read cannot be located. This may occur if the file is accessed
on a computer that does not have the class.
Software Engineering Observation 15.1
This section introduced object serialization and demonstrated basic serialization tech-
niques. Serialization is a deep subject with many traps and pitfalls. Before implementing
object serialization in industrial-strength applications, carefully read the online Java doc-
umentation for object serialization.
15.6 Opening Files with JFileChooser
Class JFileChooser displays a dialog that enables the user to easily select files or directo-
ries. To demonstrate JFileChooser , we enhance the example in Section 15.3, as shown in
Figs. 15.12-15.13. The example now contains a graphical user interface, but still displays
the same data as before. The constructor calls method analyzePath in line 24. This meth-
od then calls method getFileOrDirectoryPath in line 31 to retrieve a Path object repre-
senting the selected file or directory.
Method getFileOrDirectoryPath (lines 71-85 of Fig. 15.12) creates a JFile-
Chooser (line 74). Lines 75-76 call method setFileSelectionMode to specify what the
user can select from the fileChooser . For this program, we use JFileChooser static
constant FILES_AND_DIRECTORIES to indicate that files and directories can be selected.
Other static constants include FILES_ONLY (the default) and DIRECTORIES_ONLY .
Line 77 calls method showOpenDialog to display the JFileChooser dialog titled Open .
Argument this specifies the JFileChooser dialog's parent window, which determines the
position of the dialog on the screen. If null is passed, the dialog is displayed in the center
of the screen—otherwise, the dialog is centered over the application window (specified by
the argument this ). A JFileChooser dialog is a modal dialog that does not allow the user
to interact with any other window in the program until the dialog is closed. The user selects
the drive, directory or filename, then clicks Open . Method showOpenDialog returns an
integer specifying which button ( Open or Cancel ) the user clicked to close the dialog. Line