Java How to Program Fourth Edition - DCC

Chapter 16 Files and Streams 967
length (line 55), getPath (line 56), getAbsolutePath (line 57) and getParent
(line 58).
If the File object represents a file (line 61), the program reads the contents of the file
and displays the contents in the JTextArea. The program uses a BufferedReader
object chained to a FileReader object (lines 65–66) to open the file for reading and to
read the file one line at a time with method readLine (line 71). Note that the
FileReader object was initialized with the File object name (line 66).
If the File object represents a directory (line 86), the program reads the contents of
the directory into the program by using File method list, then displays the directory
contents in the JTextArea.
The first output demonstrates a File object associated with the jfc directory from
the Java 2 Software Development Kit. The second output of this program demonstrates a
File object associated with the readme.txt file from the Java 2 Software Development
Kit. In both cases, we specified an absolute path on our personal computer.
Note that the \ separator character is used to separate directories and files in the path.
On a UNIX workstation, the separator character would be the / character. Java processes
both characters identically in a path name. So, if we specified the path
c:\java/readme.txt
which uses one of each separator character, Java still processes the file properly.
Common Programming Error 16.2
Using \ as a directory separator rather than \\ in a string literal is a logic error. A single
\ indicates that the \ and the next character represent an escape sequence. To insert a \ in
a string literal, you must use \\. 16.2
SUMMARY
Good Programming Practice 16.6
When building Strings that represent path information, use File.separatorChar to
obtain the local computer’s proper separator character, rather than explicitly using / or \. 16.6
• All data items processed by a computer are reduced to combinations of zeros and ones.
• The smallest data item in a computer (a bit) can assume the value 0 or the value 1.
• Digits, letters and special symbols are called characters. The set of all characters used to write programs
and represent data items on a particular computer is called that computer’s character set.
Every character in a computer’s character set is represented as a pattern of 1s and 0s. (Characters
in Java are Unicode characters composed of 2 bytes.)
• A field is a group of characters (or bytes) that conveys meaning.
• A record is a group of related fields.
• At least one field in a record is chosen as a record key to identify a record as belonging to a particular
person or entity that is unique from all other records in the file.
• Java imposes no structure on a file. Notions like “record” do not exist in Java. The programmer
must structure a file appropriately to meet the requirements of an application.
• A collection of programs designed to create and manage databases is called a database management
system (DBMS).
• Java views each file as a sequential stream of bytes.