CIS 270—Application Development II

1. CIS 270—Application Development II Chapter 14—Files and Streams

2. 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)

3. 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 • one byte is composed of eight bits • ‘A’ = hex 0041 = ASCII 00001011 = Unicode 00000000 00001011 • A meaningful group of characters forms a ________. • A meaningful group of fields forms a record. • A group of related records forms a file. • 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 ____________.

4. 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)

5. 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.

6. 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

7. 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.

8. 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.

9. 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.

10. 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.