1. Comp 212: Intermediate Programming Lecture 30 – Stream and File I/O
By: Anupam Chanda

2. Today’s Menu Introduction to I/O Streams Reader and Writer Classes
StreamTokenizer and Parsing
Command-line Arguments
System Class

3. Stream I/O Stream – abstract concept of input and output
Sequence of data
Has a source or a destination
java.io package

4. Reading and Writing open(stream); while (more info) read(stream);
WRITE
open(stream);
while (more info)
read(stream);
close(stream);
open(stream);
while (more info)
write(stream);
close(stream);

5. Types of Streams Byte Streams Character Streams
Operate on bytes (8-bit)
No further discussion
Character Streams
Operate on 16-bit characters
Reader and Writer

6. Reader and Writer

7. Reader An abstract class Need a concrete subclass
Can read from an abstract character source
Need a concrete subclass
Read from a concrete character source
FileReader fReader = new FileReader(fileName);
fReader.read() – next character from source

8. Writer An abstract class Need a concrete subclass
Can write to an abstract character destination
Need a concrete subclass
Write to a concrete character source
FileWriter fWriter = new FileWriter(fileName);
fWriter.write() – next character to destination

9. Read and Write Text Files
import java.io.*;
public class Copy {
public static void main(String[] args) throws IOException {
FileReader in = new FileReader(“in.txt”);
FileWriter out = new FileWriter(“out.txt”);
int c;
while ((c = in.read()) != -1)
out.write(c);
in.close();
out.close(); }

12. StreamTokenizer and Parsing
Parse an input stream of characters
Identify words, numbers, etc.
Tokenizing – breaking an input stream in “tokens”
int k = 100;
Tokens – “int”, “k”, “=“, “100”, “;”
java.io.StreamTokenizer
Example program on web page

13. Command-line arguments
Pass arguments to the program at run-time
public static void main(String[] argv) {
for(int j = 0; j < argv.length; j++)  System.out.print(argv[j] + “ "); 
System.out.println(); }

14. Stdin, Stdout & Stderr System.out.println(“Hello world!”);
System.out – PrintStream object
Writes to standard output (stdout) – monitor
% java MyClass > out.txt
System.in – stdin (keyboard)
% java MyClass < in.txt
System.err – stderr (monitor)
% java MyClass >& err.txt
PrintStream is deprecated