08_IO in java.pdf

I/O in java

Java IO Classes

• Java I/O is based on a class hierarchy.

• Base classes are used to describe the basic functionality required.

• Derived classes provided the functionality for specific kinds of I/O environments.

2

I/O Stream

Stream A stream is an abstraction that either

produces or consumes information.

Input Streamreads or consumes information

Input Stream Sourcekeyboard or file

Output Stream writes or produces information

Output Stream DestinationsMonitor or file

Some Abstract Base Classes

•

InputStream

– for reading a stream of bytes

•

OutputStream

– for writing a stream of bytes

•

Reader

– reading a stream of characters

•

Writer

– writing a stream of characters.

Nihar Ranjan Roy ₄

Byte Oriented

Class

OutputStream

• All

byte

stream writers

are based on the class

OutputStream

(they extend

OutputStream

)

• Some of the methods:

– void write(int b) throws IOException – void write(byte[] b) throws IOException – void flush() throws IOException

– void close() throws IOException

throws IOException

• Everything here can throw an

• If you use any of these methods, you must

catch

(or

).

IOException

6

Class

Reader

• All

character

stream

readers are based on

the class

(they extend

)

• Some of the methods:

– int read()

– int read(char[] cbuf) – boolean ready()

– void close()

Class

Writer

• All character stream writers are based on the

class Writer (they extend Writer)

• Some of the methods:

– void write(int c)

– void write(char[] cbuf) – void write(String str) – void flush()

– void close()

Abstract Classes

• You can't create an InputStream object!

– or OutputStream or Reader or Writer

• You create some object of a derived class

– a specific kind of InputStream object, perhaps a FileInputStream

– but your code can be written to work with any kind of

InputStream

System.out

• System.out is actually a kind of OutputStream:

– it's a PrintStream object, but you don't need to know that to

use it as an OutputStream

OutputStream stdout = System.out; stdout.write(104); // ASCII 'h'

stdout.flush();

IOExceptions!

public static void main(String[] args) { OutputStream stdout = System.out;

try {

stdout.write(104); // 'h' stdout.write(105); // 'i' stdout.write(10); // '\n'

} catch (IOException e) { e.printStackTrace(); }

}

Another way…

public static void main(String[] args)

throws IOException {

OutputStream stdout = System.out; stdout.write(104); // 'h'

stdout.write(105); // 'i' stdout.write(10); // '\n' }

System.in

System.in

is a type of

byte[] b = new byte[10];

InputStream stdin = System.in; stdin.read(b);

Character Streams

• Remember that Java supports UNICODE!

– support for non-ASCII characters.

• Java also supports ASCII (obviously).

• BUT – since characters are not necessarily a single byte – we need more than byte streams.

InputStreamReader

• An InputStreamReader is a bridge from byte streams to

character streams.

– You need to have an InputStream to feed the InputStreamReader.

• Each call to InputStreamReader.read() returns one char,

but may read multiple bytes from the InputStream.

InputStreamReader

attached to

stdin

InputStreamReader isr = new

InputStreamReader( System.in );

char c;

c = (char) isr.read(); System.out.write( c);

BufferedReader

• A type of

that does internal buffering.

– more efficient.

• Provides everything from

, plus:

String readLine()

– String returned does not include the line termination char(s).

Attaching a

BufferedReader

to stdin

InputStreamReader isr = new

InputStreamReader(System.in);

BufferedReader bf = new BufferedReader(isr);

String foo = bf.readLine();

Character Stream Output

• OutputStreamWriter: a bridge (converts from characters

to byte stream).

• BufferedWriter: efficient Writer.

BufferedWriter bw =

new BufferedWriter(

new OutputStreamWriter ( System.out ) );

File Handling

Create a file object

package required is Import java.io.*;

File inFile=new File(“C:\\abc.dat”);

Or

File inFile=new File(“c:\\myfolder”,”abc.txt”);

boolean exists() Tests whether the file or directory denoted by this abstract pathname exists.

void deleteOnExit() Requests that the file or directory denoted by this abstract pathname be deleted when the virtual machine terminates.

boolean _{canExecute()  Tests whether the application can execute the} file denoted by this abstract pathname.

boolean canRead()  Tests whether the application can read the file denoted by this abstract pathname.

boolean _{canWrite()  Tests whether the application can modify the file} denoted by this abstract pathname.

boolean delete()  Deletes the file or directory denoted by this abstract pathname.

String getName()  Returns the name of the file or directory denoted by this abstract pathname.

String getParent() Returns the pathname string of this abstract pathname's parent, or null if this pathname does not name a parent directory.

boolean _{isDirectory()  Tests whether the file denoted by this abstract} pathname is a directory.

booleanisFile()  Tests whether the file denoted by this abstract pathname is a normal file.

booleanisHidden() Tests whether the file named by this abstract pathname is a hidden file.

long_{lastModified()  Returns the time that the file denoted by this} abstract pathname was last modified.

long_{length() Returns the length of the file denoted by this abstract} pathname.

boolean _{mkdir()  Creates the directory named by this abstract} pathname.

String[] _{list()  Returns an array of strings naming the files and}

directories in the directory denoted by this abstract pathname.

Problem

Write a program in java that

prints all the files in a

specified directory

Listing all files from a directory

File mydir=new File(“c:\\javaprgs”);

String fileList[] = mydir.list();

for(int i=0; i<fileList.length; i++)

System.out.println( fileList[i] );

Nihar Ranjan Roy ₂₅

FileInputStream

• Class FileInputStream

• java.lang.Object

– java.io.InputStream

• java.io.FileInputStream

FileInputStream is meant for reading streams

of raw bytes such as image data

FileInputStream

(

File

file)

FileInputStream

(

String

name)

Few Methods

Nihar Ranjan Roy ₂₇

int _{read() }

Reads a byte of data from this input stream.

int _{read(byte[] b)  Reads up to b.length bytes of data from this} input stream into an array of bytes.

int _{read(byte[] b, int off, int len)  Reads up to len bytes of data} from this input stream into an array of bytes.

Problem

Write a program in java in

which the program prints its

source code.

import java.io.*;

class ReadFromFile {

public static void main(String args[])

throws IOException { int ch;

FileInputStream fo=new

FileInputStream("c:\\myJava\\ReadFromFile.java"); while((ch=fo.read())!=-1)

{ System.out.print((char)ch); }

fo.close(); }

}

Writing to a file

• Class is FileOutPutStream

• FileOutputStream is meant for writing streams of raw bytes such as image data. For writing streams of characters, consider using FileWriter.

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Constructor Summary

FileOutputStream(File file)

Creates a file output stream to write to the file represented by the specified File object.

FileOutputStream(File file, boolean append)

Creates a file output stream to write to the file represented by the specified File object.

FileOutputStream(String name)

Creates an output file stream to write to the file with the specified name.

FileOutputStream(String name, boolean append)

Some Methods

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void write(byte[] b)

Writes b.length bytes from the specified byte array to this file output stream.

void write(byte[] b, int off, int len)

Writes len bytes from the specified byte array starting at offset off to this file output stream.

void _{write(int b)}

Writes the specified byte to this file output stream.

void _close()

Problem

Write a program in java to copy a

file

myCopy sourceFile DestationFile

Class FileReader

• java.lang.Object

– java.io.Reader

• java.io.InputStreamReader

– java.io.FileReader

FileReader is meant for reading streams of

characters. For reading streams of raw bytes, consider using a FileInputStream.

Constructor Summary

FileReader ( File file)

FileReader ( String fileName)

Print the Source Code using FileReader

import java.io.*;

class FileReaderTest

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

FileReader fr=new FileReader("FileReaderTest.java"); BufferedReader br=new BufferedReader(fr);

String str=null;

while((str=br.readLine())!=null) {System.out.println(str); }

} }

Class FileWriter

java.lang.Object java.io.Writer

java.io.OutputStreamWriter

java.io.FileWriter

FileWriter is meant for writing streams of characters. For writing streams of raw bytes, consider using a FileOutputStream.

Constructor Summary

FileWriter(File file)

FileWriter(File file, boolean append)

FileWriter(String fileName)

FileWriter(String fileName, boolean append)

Problem

Write a program in java that asks the use to enter something about him. What ever the user enters it should be stored in to a file.

Nihar Ranjan Roy ₃₇

import java.io.*;

class FileWriterTest

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

FileWriter fw=new FileWriter("FileWriter.dat"); BufferedReader br=new BufferedReader(new InputStreamReader(System.in));

int ch;

System.out.println("Please enter something about u"); while((ch=br.read())!=-1)

{ fw.write(ch);

}

fw.close();

System.out.println("Done Successfully"); }

DataOutputStream

DataOutputStream object

defines the methods used to write primitive data types

to output streams

Constructor Summary

DataOutputStream( OutputStream out)

Creates a new data output stream to write data to the specified underlying output stream.

Nihar Ranjan Roy ₃₉

void writeBoolean(boolean v) void writeByte(int v)

void writeBytes( String s) void writeChar(int v)

void writeChars( String s) void writeDouble(double v) void writeFloat(float v)

void writeInt(int v)

Writing Primitives Data types to file

import java.io.*;

class PrimitiveWrite

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

DataOutputStream dos=

new DataOutputStream(

new FileOutputStream("Primitive.dat")); dos.writeInt(23);

dos.writeBoolean(true); dos.close();

} }

DataInputStream

A DataInputStream lets an application read primitive Java data types from an underlying input stream in a machine-independent way

Constructor Summary

DataInputStream ( InputStream in)

Creates a DataInputStream that uses the specified underlying InputStream.

Nihar Ranjan Roy ₄₂

boolean readBoolean() byte readByte()

char readChar() double readDouble() float readFloat() int readInt() long readLong() short readShort()

Use of DataInputStream

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import java.io.*;

class PrimitiveRead {

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

DataInputStream dis=

new DataInputStream(

new FileInputStream("Primitive.dat")); System.out.println(dis.readInt());

System.out.println(dis.readBoolean()); dis.close();

Problem

Write a program in java that accepts students details NameString

Rollint

stores them to a file “student.dat”

Writing objects to file

Nihar Ranjan Roy ₄₅

class Student implements Serializable {

String name; int roll;

Writing objects to file

Nihar Ranjan Roy ₄₆

import java.io.*; class writeObject {

public static void main(String args[]) throws Exception {Student st=new Student("Nihar",143);

ObjectOutputStream oos=

new ObjectOutputStream(

new FileOutputStream("Object.dat"));

oos.writeObject(st);

System.out.println("Written Successfully"); oos.close();

Reading objects from file

Nihar Ranjan Roy ₄₇

import java.io.*; class readObject {

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

ObjectInputStream ois=

new ObjectInputStream(

RandomAccessFile

• RandomAccessFile in java enables us to read and

write bytes, text and java data types to any location in a file.

• The term random means data can be written or read from random location within a file.

• This class also provides permissions like read and

write and allows files to be accessed in read only and read write mode.

• Two ways to create the file

RandomAccessFile(File name,String mode) or

RandomAccessFile(String pathname,String mode)

Modes

”r” read only

”rw” read and write.

We can read or write the primitive data types through readXXX() and writeXXX() methods

Nihar Ranjan Roy ₅₀

class randomAccessFile {

Sequence InputStream

A SequenceInputStream represents the logical concatenation of multiple input streams.

It starts out with an ordered collection of input

streams and reads from the first one until end of file is reached, whereupon it reads from the second one, and so on, until end of file is reached on the last of the

contained input streams.

SequenceInputStream( InputStream s1, InputStream s2)

Problem

Write a program in java that takes two file names as command prompts and reads the files in the same order once the first file is finished it starts reading the second one.

Nihar Ranjan Roy ₅₂

HINT

FileInputStream f1=new FileInputStream(args[0]) FileInputStream f2=new FileInputStream(args[1])

SequenceInputStream sis=new SequenceInputStream(f1,f2);