Java How to Program Fourth Edition - DCC

920 Files and Streams Chapter 16
Fig. Fig. 16.8 16.8 Reading a sequential file (part 6 of 6).
Most of the code in this example is similar to Fig. 16.6, so we discuss only the key lines
of code that are different. Line 105 calls JFileChooser method showOpenDialog to
display the Open dialog (second screen capture in Fig. 16.8). The behavior and GUI are
the same as the dialog displayed by showSaveDialog, except that the title of the dialog
and the Save button are both replaced with Open.
Lines 125–126 create a ObjectInputStream object and assign it to input. The
File fileName is passed to the FileInputStream constructor to open the file.
The program reads a record from the file each time the user clicks the Next Record
button. Line 84 in Next Record’s actionPerformed method calls method
readRecord (lines 144–187) to read one record from the file. Line 150 calls method
readObject to read an Object from the ObjectInputStream. To use AccountRecord
specific methods, we cast the returned Object to type AccountRecord. If
the end-of-file marker is reached during reading, readObject throws an EndOfFile-
Exception.
To retrieve data sequentially from a file, programs normally start reading from the
beginning of the file and read all the data consecutively until the desired data are found. It
might be necessary to process the file sequentially several times (from the beginning of the
file) during the execution of a program. Class FileInputStream does not provide the
ability to reposition to the beginning of the file to read the file again unless the program
closes the file and reopens it. Class RandomAccessFile objects can reposition to the
beginning of the file. Class RandomAccessFile provides all the capabilities of the