Transcript CIS 397—Web Design

CIS 270—Application
Development II
Chapter 14—Files and Streams
14.1 Introduction



Data maintained in files are called ___________ and
are stored on secondary storage devices.
A _________ is ordered data read from or written to
a file.
Three forms of file processing with Java



text file (storing text)
object serialization (storing objects)
random-access (for use with databases)
2
14.2 Data Hierarchy

A single electronic circuit can store a bit (_______
digit) with possible values of 0 or 1 (off or on).


Humans use decimal digits, letters, and other symbols.
Data hierarchy

Characters in Java are in __________ that uses two bytes





A meaningful group of characters forms a ________.
A meaningful group of fields forms a record.
A group of related records forms a file.



one byte is composed of eight bits
‘A’ = hex 0041 = ASCII 00001011 = Unicode 00000000 00001011
One or more fields in a record can form a primary key that uniquely
identifies a record (e.g. a social security number).
A sequential data file stores records in primary key order.
A group of related files forms a ____________.
3
14.3 Files and Streams 1






Java views a file as a ____________ stream of bytes.
An operating system uses an end-of-file ________.
A stream can perform ____ in bytes (a byte-based
stream) or characters (a character-based stream).
Files created using byte-based streams are called
________ files (which must be converted to text).
Files created using character-based streams are
called _____ files (which can be read by text editors).
Three Java stream objects that can be redirected.



System.in (standard input stream from the keyboard)
System.out (standard output stream to the screen)
System.err (standard error stream to the screen)
4
14.3 Files and Streams 2

File processing classes are in the package
_________:





FileInputStream and FileOutputStream for ______based file I/O
FileReader and FileWriter for character-based file
I/O
Object I/O is handled by ObjectInputStream and
ObjectOutputStream.
Class File provides information about files and
___________.
Classes Scanner and Formatter can also perform
character-based input and output, respectively. 5
14.4 Class File



An absolute path is the location of a file or directory
starting with the ______ directory.
A _________ path is the location of a file or directory
starting where the application began executing.
A URI (Uniform Resource Identifier) can be used to
locate a file, such as with file:/C:/data.txt in
Windows.


A URL is used to locate web sites, http://www.sun.com.
A ___________ character separates directories and
files in a path

\ for Windows, / for UNIX—Java interprets each the same
6
14.5 Sequential-Access Files






Java imposes no structure on a file (such as
records). This must be done by the application.
Trying to write to a non-existent file will create the
file.
Trying to write to an existing file will _________ the
existing file (existing data will be discarded).
By default, all data files are assumed to be in the
same directory as the application files.
See Figs. 14.6-14.7 for a writing example.
See Figs. 14.11-14.12 for a reading example.
7
14.6 Object Serialization




Data written to a text files loses information about
their ______ (int, String, double, etc.) and the
type of object containing these data.
A serialized object is a sequence of bytes that
includes this information.
These data can be read from a file and ___________
into an object in memory.
Classes ObjectInputStream and
ObjectOutputStream implement the interfaces
ObjectInput and ObjectOutput and use file
stream classes FileInputStream and
FileOutputStream.
8
14.6.1 Reading / Writing Objects
from / to a File





An object-defining class (ODC) must implement
Serializable to serialize and deserialize objects.
All _________ variables of the ODC must be
serializable (primitives and arrays are by default).
________ occurs when an object-stream object uses
a file-stream object to read/write objects to a file.
See Figs. 14.17-14.19 for an example of writing
objects to a file.
See Figs. 14.20-14.21 for an example of reading
objects from a file.
9
14.7 Random-Access Files


Sequential-access files are suited for _______
applications.
Instant-access applications, such as transaction
processing systems, need rapid access to data.



These applications need random-access files.
Random-access files are also called _______-access files.
See program examples in text.
10