1. 18
File i/o, Parsing

2. Previously Defining Classes Inheritance of Properties
Inheritance of Methods
Sub and super classes

3. Overview
File & Streams
Read
Write
Parsing

4. File i/o i/o refers to input and output
File i/o refers to the process of
Reading file information
Reading from a file
Writing to a file
Type of files are
Directories
Archives usually called files

5. File Types Two types of file: Text Binary
Files composed only of ASCII / Unicode characters
Binary
Files that may contain any type of data
Archives - jar/zip files
Programs - executable file
Media - Images / Sound / Movie

6. Contents of a Binary File
Open with a text editor

7. File API
File is a class
Part of the java.io package
File instances (objects) represent a file or directory in the system
File instances (objects) do not provide access to the file content
File class provides useful methods to retrieve information about a file or directory
isDirectory(), isFile(), exists(), canRead(), canWrite(),…
All i/o must be error trapped (i.e. a file can only be opened inside a try statement).

8. File Paths Relative Absolute Systems Separator
From where Program is running
Absolute
Full Path
Systems
POSIX
/home/axmh03/public_html/test.txt
Windows
C:\Documents and Settings\axmh03\docs\test.txt
Separator
String separator = File.separator;
String separator = FileSystems.getDefault().getSeparator();

9. File Constructors
You can create a new empty directory / file object using the File constructor:
File dir = new File(".\images");
File img1 = new File(dir, "logo.gif");
File img2 = new File(".\images\logo.gif");
File img3 = new File(".\images", "logo.gif");
File objects can be EITHER directories OR files

10. File Management Some useful methods
public boolean exists()
true if the file exists and false otherwise
public boolean createNewFile() throws IOException
true if the new file was created (does not already exists) or false otherwise
public boolean delete() throws SecurityException
true if the file or directory is successfully deleted or false otherwise

11. Accessing File Contents
FileReader
Assumes the default character encoding
If different character encoding use class InputStreamReader
FileWriter
If different character encoding use class InputStreamWriter
Buffered Streams:
BufferedReader
BufferedWriter

12. Parsing Text: Scanner We've already used to intercept keyboard input
Can also be used to read in a file and separate into tokens
By default separated on whitespace
Can change delimiter invoking useDelimiter()
By default tokens are a String but there are methods to read in most basic types

13. Vectors Like an Elastic Array of Objects
Generally need to cast from generic type
Useful for returning lists of things
Java.util.Vector
Vector<ObjectType> stuff = new Vector<ObjectType>();