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Streams

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Title: Streams

1
Streams

CSC 171 FALL 2004
LECTURE 22

2
Make up exam

Friday 12/3 11AM-1210PM

3
READING ASSIGNMENT

Horstmann Chapter 15 Streams
Horstmann Chapter 14 Exceptions
Optional
Horstmann Chapter 16 System Design
Horstmann Chapter 17, 18, 19
Prep for CSC 172

4
EXAM

In class 12/9
Arrays
Exceptions
Streams

5
Streams

In Java a stream provides access to sequences of
bytes.
Bytes can come from a variety of sources
Console input/output
Files stored on the computers disk
Network connections

_________ access sequences of bytes.

___Streams______ access sequences of bytes.

8
Simplest File input

Create a FileReader
Use its read method to read a single
character-returns the next char as an int or the
integer -1 at end of input
Test for -1
If not -1, cast to char
Close the file when done

___________ and ________________ access sequences
of characters.

_readers______ and ____writers____ access
sequences of characters.

11
Reading

FileReader reader new FileReader("input.txt")
int next reader.read()
char c
if (next ! -1)
c (char)next()
...
reader.close()

12
Writing

FileWriter writer new FileWriter("output.txt")
...char c''...writer.write(c)
...write.close()

The read method returns an _________________,
either ___________ at end of file, or another
value which needs to be cast to ___________, or
___________.

The read method returns an ___integer_____,
either ____-1_______ at end of file, or another
value which needs to be cast to ___char____, or
____byte_______.

You must _______________ files that you no longer
need.

You must ___close______ files that you no longer
need.

17
(No Transcript)
18
TEXT FORMAT

Human-readable form
Sequence of characters-Integer 12345 stored as
characters "1" "2" "3" "4" "5"
Use Reader and Writer and their subclasses

19
Writing text files

Use a PrintWriter -breaks up strings into
individual characters -sends them one at a time
to a FileWriter
Create a PrintWriter
FileWriter writer new FileWriter("output.txt")
PrintWriter out new PrintWriter(writer)
Use print and println
out.println(29.95)
out.println(new Rectangle(5,10,15,25))
out.println("Hello, World!")

Use a BufferedReader -Reads a character at a
time from a FileReader-Assembles the characters
into a line and returns it
Use Integer.parseInt or Integer.parseDouble to
convert the strings to numbers
Code
FileReader reader new FileReader ("input.txt")
BufferedReader in new BufferedReader(reader)
String inputLine in.ReadLine()
double x Double.parseDouble(inputLine)

Basic streams, readers, and writers can process
only _____________________. You need to combine
them with other classes to process
_______________ or _________________.

Basic streams, readers, and writers can process
only _individual bytes or chars______. You need
to combine them with other classes to process
___lines______ or ____objects______.

When writing text files, use ________________
class and the _____________________ methods.
When reading text files, use _______________
class and the ____________ method.

When writing text files, use _____PrintWriter_____
_ class and the ____print/println__________
methods.
When reading text files, use _____BufferedReader__
______ class and the ___readLine______ method.

25
File

File class describes disk files and directories
Create a File objectFile inputFile new
File("input.txt")
Some file methods
delete
renameTo
exists
Constructing a FileReader from a File object
FileReader reader new FileReader(inputFile)

A File object describes a ___________ or
__________________.

A File object describes a _____file_______ or
_______directory___________.

You can pass a File object to the constructor of
a file ____________, _________, or stream.

You can pass a File object to the constructor of
a file ____reader_________, ___writer________, or
stream.

30
File Chooser
31
File Choser

Construct a file chooser object
Call its showOpenDialog or showSaveDialog method
Specify null or the user interface component over
which to pop up the dialog
If the user chooses a file, these methods return
JFileChooser.APPROVE_OPTION
If the user cancels the selection, these methods
return JFileChooser.CANCEL_OPTION
If a file is chosen, use GetSelectedFile method
to obtain a File object describing the file

32
Code

JFileChooser chooser new JFileChooser()
FileReader in null
if (chooser.showOpenDialog(null)
JFileChooser.APPROVE_OPTION)
File selectedFile chooser.getSelectedFile()
in new FileReader(selectedFile)

The ______________________________ dialog lets
users select a file by navigating directories.

The _JFileChooser__________ dialog lets users
select a file by navigating directories.

35
Command Line

Java MyProgram -d file.txt
class MyProgram
public static void main(String args) ...
// arg0 -d
// arg1 file.txt

When you launch a program from the command line,
you can specify arguments after the program name.
The program can access these strings by
processing the ______________ parameter of the
___________ method.

When you launch a program from the command line,
you can specify arguments after the program name.
The program can access these strings by
processing the _____args___ parameter of the
___main___ method.

38
Binary Format