I/O

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FILE

1    File is a collection of data stored in a particular area on the disk.

2    File is used to  read and write operations on the file.

3    A file program involves either or both of the following kinds of data communication.

1.  Data transfer b/w the console unit and the program.

2.  Data transfer b/w the program and a disk file.

I/p:

Keyboardàconsole

Consoleàfile

Fileàclass

O/p:

Classàfile

Fileàconsole

Consoleàdisplay

File is class of the java.io package that references an actual disk file.

File obj=new File(“path,file-name”);

File Obj=new File(“filename”);

Methods

getName()               à   Returns the name of the file

getAbsolutePath()    à   Returns the name of the parent directory

getParent()               à   Returns the directory only

getModified()            à   if it is modified or not

isHidden()                 à   Returns if the file hidden or not

canWrite()                à   Returns if the file is writable or not

canRead()                à   Returns if the file is readable or not

exist()                       à   Returns true if the file is exist or not false

isFile()                      à   Returns if it is file

isDirectory()             à   Returns if it is directory

length()                    à   Find the length of the string

Example for above methods:

import java.io.*;

class fdetail

{

public static void main(String s[])

{

//File ob=new File("c:/ani/abs.java");

File ob=new File(s[0]);

if(ob.exists())

{                              

System.out.println(ob.getName());

System.out.println(ob.getPath());

System.out.println(ob.getParent());

System.out.println(ob.getAbsolutePath());

System.out.println(ob.canRead()?"Readble":"not Readble");

System.out.println(ob.canWrite()?"Writable":"not Writable");

System.out.println(ob.isHidden()?"Hidden":"not Hidden");

System.out.println(ob.lastModified());

System.out.println(ob.isFile());

System.out.println(ob.isDirectory());

System.out.println(+f1.length());

}

else

System.out.println("File not Found");

}

}

}

com: javac fdetail.java

run:  java fdetail anu.txt

/* mkdir() --> to Create a Directory */

import java.io.*;

class mkd

{

public static void main(String s[])

{

File ob=new File(s[0]);

if(ob.mkdir())

        System.out.println("created");

else

        System.out.println("Already exist");

}

}

Example :

import java.io.*;

class dirdemo

{

public static void main(String s1[])

{

File ob=new File(s1[0]);

String start=s1[1];

String end=s1[2];

if(ob.isDirectory()) 

{

        String s[] = ob.list();

                   

        for(int i=0;i<s.length;i++)

                if(s[i].endsWith(end))

                  if (s[i].startsWith(start))

                        System.out.println(s[i]+"\t");

}

else

        System.out.println("Not a Directroy");

}

}

com: javac  dirdemo.java

run: java dirdemo pack p java

p1.java

p2.java

pack.java

packàdirectory

pàfile name represent

javaàextension

Streams

A Stream is a path of communication between the source and destination.

Stream are divided into 4 abstract classes

1.  Input stream

2.  Output stream

3.  Reader

4.  Writer

·       The I/o and o/p are designed byte stream

·       Reader and Writer are designed for characters stream

·       Byte stream classes and the character stream classes

    Form separate hierarchy

Byte Stream:

1. The byte stream classes provide a rich environment for   

     handling byte oriented I/O.

2. A byte stream can be used with any type of object

        including binary data.

File InputStream 

Class helps in reading data from the actual disk file.

FileInputStream o=new FileInputstream(string name);

FileInputStream o=new FileInputstream(File-obj);

Methods

Int read() àReturns and integer representation of the next available byte of I/p, -1 is return when the end of the file is 0ncountered.

available()àReturns the number of bytes that can be read from the file input stream.

close()àCloses the file input stream and releases any system resources associated with the stream.

Skip(long value)  àskip from specified value

import java.io.*;

class Fdemo

{

public static void main(String ar[])throws Exception

{

int t,i;

File ob=new File(ar[0]);

if(ob.exists())

{

FileInputStream in=new FileInputStream(ob);

t=in.available();

        System.out.println("Available:"+ t);

for(i=0;i<200;i++)

        System.out.print((char)in.read());

         System.out.println("\nAvailable:"+ in.available());

in.skip(400);

        System.out.println("Available:"+ ( t=in.available()) );

        while(in.read()!=-1)

               System.out.print((char)in.read());

               in.close();

   }

else

        System.out.println("File not Found");

}

}

run:  java fdemo fr.java

FileOutputStream

class helps to create a file and write data into it using the methods of the OutputStream class.

FileOutputStream ob=new FileOutputStream(“filename”,true);

Methods

write()              -       Writes the specified byte to the file output stream.

// FileOutputStream

import java.io.*;

class fwrite

{

public static void main(String s[])throws Exception

{

String st="This File Write Program";

int i,c;

FileOutputStream out=new FileOutputStream(s[0],true);

for(i=65;i<91;i++)

out.write(i);

out.write('\n');

do

{

c=System.in.read();

out.write(c);

}while(c!='#');

out.close();

              

out=new FileOutputStream(s[1]);

byte b[]=st.getBytes();

out.write(b,0,9);

out.write('\n');

out.write(b);

out.close();

}

}

Run:

Java fwrite  a1 a2

Hai

#

à

         type a1

         type a2

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