Io Java Ver2

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I/O Basics

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Aside from print( ) and println( ), none of the

I/O methods have been used significantly. The

reason is simple: most real applications of Javaare not text-based, console programs.

they are graphically oriented programs that rely

upon Javas Abstract Window Toolkit (AWT) forinteraction with the user.

Javas support for console I/O is limited andsomewhat awkward to use even in simple

example programs. Text-based console I/O is

just not very important to Java programming.

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Streams Java programs perform I/O through streams.

A stream is an abstraction that eitherproduces or

consumes information.

A stream is linked to a physical device by the Java

I/O system. All streams behave in the same manner, even if the

actual physical devices to which they are linked

differ.

Same I/O classes and methods can be applied to

any type of device.

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Streams(contd.) Input stream can abstract many different kinds of

input: from a disk file, a keyboard, or a networksocket.

Output stream may refer to the console, a disk file,

or a network connection. Streams deal with input/output without having every

part of your code understand the difference

between a keyboard and a network.

Java implements streams within class hierarchiesdefined in thejava.io package.

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Byte Streams and Character Streams Java 2 defines two types of streams: byte and

character. Byte streams providemeans for handling input and

output of bytes and are used for reading or writing

binary data.

Character streams handle input and output ofcharacters. They use Unicode and, therefore, can

be internationalized.

In some cases, character streams are more efficientthan byte streams.

At the lowest level, all I/O is byte-oriented

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The Byte Stream Classes

Byte streams are defined by using two class

hierarchies. At the top are two abstract classes:InputStream and OutputStream.

Each of these abstract classes has several concrete

subclasses, that handle the differences between

various devices, such as disk files, networkconnections, and even memory buffers.

to use the stream classes, you must importjava.io.

The abstract classes InputStream andOutputStream define several key methods that the

other stream classes implement. Two of the most

important are read( ) and write( ),

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which, respectively, read and write bytes of data.

Both methods are declared as abstract inside

InputStream and OutputStream.

They are overridden by derived stream classes.

The Character Stream Classes

Character streams are defined by using two class

hierarchies.

At the top are two abstract classes, Readerand

Writer, which define several key methods that theother stream classes implement.

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These abstract classes handle Unicode character

streams.

Java has several concrete subclasses of each ofthese.

Two of the most important methods are read( ) and

write( ), which read and write characters of data,

respectively.

These methods are overridden by derived stream

classes

First slide is Byte Stream classes Second slide is the character stream I/O classes

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The Predefined Streams java.lang package defines a class called System,

which encapsulates several aspects of the run-timeenvironment.

Using some of its methods, you can do the settings

of various properties associated with the system. System also contains three predefined stream

variables, in, out, and err.

These fields are declared as public, static and final

within System.

They can be used by any other part of the program

and without reference to a specific System object.

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System.out refers to the standard output stream. By

default, this is the console.

System.in refers to standard input, which is the

keyboard by default.

System.errrefers to the standard error stream, which

also is the console by default.

These streams may be redirected to any compatibleI/O device.

System.in is an object of type InputStream

System.out and System.errare objects of typePrintStream.

These are byte streams, used to read and write

characters from and to the console.

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Reading Console Input Console input is accomplished by reading from

System.in. To obtain character-based stream that is attached to

the console, you wrap System.in in a

BufferedReaderobject.

BuffereredReadersupports a buffered input stream.

Constructor is shown here:

BufferedReader(ReaderinputReader)

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System.in refers to an object of type InputStream,

it can be used forinputStream.

The following line of code creates aBufferedReaderthat is connected to the keyboard: BufferedReader br = new BufferedReader(new

InputStreamReader(System.in));

After this statement executes, bris a character-based stream that is linked to the console through

System.in.

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Reading Characters

To read a character from a BufferedReader, use

read( ).

int read( ) throws IOException

It reads a character from the input stream and

returns it as an integer value.

It returns1 when the end of the stream isencountered. It can throw an IOException.

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// Use a BufferedReader to read characters from the console.

import java.io.*;

class BRRead {

public static void main(String args[]) throws IOException {char c;

BufferedReader br = new

BufferedReader(new InputStreamReader(System.in));

System.out.println("Enter characters, 'q' to quit.");

// read charactersdo {

c = (char) br.read();

System.out.println(c);

} while(c != 'q');}

}

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Enter characters, 'q' to quit.

123abcq

1

2

3

a

bc

q

System.in is line buffered, by default. This means that no

input is actually passed to the program until you pressENTER.

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//Read a string from console using a BufferedReader

import java.io.*;

class BRReadLines {

public static void main(String args[]) throws IOException {// create a BufferedReader using System.in

BufferedReader br = new BufferedReader(new


String str;

System.out.println("Enter lines of text.");

System.out.println("Enter 'stop' to quit.");

do {

str = br.readLine();

System.out.println(str);} while(!str.equals("stop"));

}

}

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import java.io.*; //A tiny Editor

class TinyEdit {

public static void main(String args[]) throws IOException {

// create a BufferedReader using System.inBufferedReader br = new BufferedReader(new


String str[] = new String[100];

System.out.println("Enter lines of text.");

System.out.println("Enter 'stop' to quit.");

for(int i=0; i


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Here is a sample run:

Enter lines of text.

Enter 'stop' to quit.This is line one.

This is line two.

Just create String objects.stop

Here is your file:

This is line one.

This is line two.

Just create String objects

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Writing Console Output

PrintStream is an output stream derived fromOutputStream, it implements the low-level

method write( ).

write( ) can be used to write to the console:

void write(int byteval)

This method writes to the stream the byte

specified by byteval.

byteval is declared as an integer, only the low-order eight bits are written.

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class WriteDemo {

public static void main(String args[]) {

int b;

b = 'A';

System.out.write(b);

System.out.write('\n');

}

}

Writes A to the console and adds a new line.

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Reading and Writing Files In Java, all files are byte-oriented

FileInputStream and FileOutputStream create bytestreams linked to files

To open a file, create an object of one of these classes,

specifying the name of the file as an argument to the

constructor

FileInputStream (String fileName) throws

FileNotFoundException

FileOutputStream (String fileName) throws

FileNotFoundException

void close( ) throws IOException

int read( ) throws IOException

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/* Display a text file. Specify the name of the file that you want

to see. For example, to see a file called TEST.TXT, use the

following command line.

java ShowFile TEST.TXT */

import java.io.*;

class ShowFile {


int i;

FileInputStream fin;

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try {

fin = new FileInputStream(args[0]);

} catch(FileNotFoundException e) {

System.out.println("File Not Found");return;

} catch(ArrayIndexOutOfBoundsException e) {

System.out.println("Usage: ShowFile File");

return;

}

// read characters until EOF is encountered

do {

i = fin.read( );

if(i != -1) System.out.print((char) i);} while(i != -1);

fin.close( );

}

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To write to a file, use write( ) method defined by

FileOutputStream.

void write(int byteval) throws IOException

/* Copy a text file. To use this program, specify the name of the

source file and the destination file.

For example, to copy a file called FIRST.TXT to a file calledSECOND.TXT, use the following command line.

java CopyFile FIRST.TXT SECOND.TXT

*/

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import java.io.*;

class CopyFile {


int i;FileInputStream fin;

FileOutputStream fout;

try {

//open input file

try {

fin = new FileInputStream(args[0]);

} catch(FileNotFoundException e) {

System.out.println("Input File Not Found");

return;}

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//open output file

try {

fout = new FileOutputStream(args[1]);

} catch(FileNotFoundException e) {System.out.println("Error Opening Output File");

return;

}

} catch(ArrayIndexOutOfBoundsException e) {

System.out.println("Usage: CopyFile From To");

return;

}

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//Copy File

try {

do {

i = fin.read( );

if(i != -1) fout.write(i);

} while(i != -1);

} catch(IOException e) {

System.out.println("File Error");

}

fin.close();

fout.close();}

}

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