Comp 212: Intermediate Programming Lecture 30

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Comp 212 Intermediate ProgrammingLecture 30
Stream and File I/O

• By Anupam Chanda

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Todays Menu

• Introduction to I/O Streams
• Reader and Writer Classes
• StreamTokenizer and Parsing
• Command-line Arguments
• System Class

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Stream I/O

• Stream abstract concept of input and output
• Sequence of data
• Has a source or a destination
• java.io package

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Reading and Writing
READ
WRITE

• open(stream)
• while (more info)
• read(stream)
• close(stream)

open(stream) while (more info) write(stream) cl
ose(stream)
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Types of Streams

• Byte Streams
• Operate on bytes (8-bit)
• No further discussion
• Character Streams
• Operate on 16-bit characters
• Reader and Writer

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Reader and Writer
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Reader

• An abstract class
• 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

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Writer

• An abstract class
• 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

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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()

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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

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Command-line arguments

• Pass arguments to the program at run-time
• public static void main(String argv)
• for(int j 0 j lt argv.length j)
   System.out.print(argvj ") 
• System.out.println()

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Stdin, Stdout Stderr

• System.out.println(Hello world!)
• System.out PrintStream object
• Writes to standard output (stdout) monitor
• java MyClass gt out.txt
• System.in stdin (keyboard)
• java MyClass lt in.txt
• System.err stderr (monitor)
• java MyClass gt err.txt
• PrintStream is deprecated