Various types of File Operations in Java

Dr.Ranjitha M
Department of Computer Science[PG]
Kristu Jayanti College, Bengaluru
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Kristu Jayanti College

Files and operations in Java
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java.io package
• java.io package contains almost every class you need to perform
input and output (I/O) in Java.
• Java programs perform I/O through streams.
• A stream is an abstraction that either produces 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.
3

java.io package
• Same I/O classes and methods can be applied to different types of
devices.
• input stream can abstract many different kinds of input: from a disk file, a
keyboard, or a network socket.
• Streams are a clean way to deal with input/ output without having
every part of your code understand the difference between a
keyboard and a network.
4

File operations
• Two of the most often-used stream classes are FileInputStream and
FileOutputStream
• Toopen a file, you simply 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
• FileNotFoundException is a subclass of IOException.
• When an output file is opened, any preexisting file by the same name
is destroyed.
5

File operations
• When you are done with a file, you must close it.
• This is done by calling the close( ) method, which is implemented by
both FileInputStream and FileOutputStream.
void close( ) throws IOException
• Closing a file releases the system resources allocated to the file,
allowing them to be used by another file.
• Failure to close a file can result in “memory leaks” because of unused
resources remaining allocated.
6

File operations
• Toread from a file, you can use a version of read( ) that is defined
within FileInputStream.
int read( ) throws IOException
• Each time that it is called, it reads a single byte from the file and
returns the byte as an integer value.
• read( ) returns –1 when the end of the file is encountered.
• It can throw an IOException.
7

File operation in Java
import java.io.*;
class ShowFile {
public static void main(String args[]) throws IOException {
int i;
FileInputStream fin;
if(args.length != 1) {// First, confirm that a filename has been specified.
System.out.println("Usage: ShowFile filename");
return;
}
try { // Attempt to open the file.
fin = new FileInputStream(args[0]);
} catch(FileNotFoundException e) {
System.out.println("Cannot Open File");
return;
}
// At this point, the file is open and can be read.
try { // The following reads characters until EOF is encountered.
do {
i = fin.read();
if(i != -1)
System.out.print((char) i);
} while(i != -1);
} catch(IOException e) {
System.out.println("Error Reading File");
}
try { // Close the file
fin.close();
System.out.println("Error Closing File");
}
}
}
8

import java.io.*;
class ShowFile {
int i;
FileInputStream fin = null;
if(args.length != 1) {// First, confirm that a filename has been specified.
System.out.println("Usage: ShowFile filename");
return;
}
try { // Attempt to open the file.
do {
i = fin.read();
if(i != -1)
System.out.print((char) i);
} while(i != -1);
}
catch(FileNotFoundException e)
{ System.out.println("Cannot Open File");
return;
System.out.println("Error Reading File");
}
finally {
// Close file in allcases.
try {
if(fin != null) fin.close();
System.out.println("Error Closing File");
}
}// End finally
}//End main
}//End class
9

File operations
• Towrite to a file, you can use the write( ) method defined by
FileOutputStream.
void write(int byteval) throws IOException
• This method writes the byte specified by byteval to the file.
• Although byteval is declared as an integer, only the low-order eight
bits are written to the file.
• If an error occurs during writing, an IOException is thrown.
1
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import java.io.*; class
CopyFile {
int i;
FileInputStream fin = null;
FileOutputStream fout = null;
// First, confirm that both files have been specified.
if(args.length != 2) {
System.out.println("Usage: CopyFile from to");
return; }
try { // Attempt to open the files.
fout = new FileOutputStream(args[1]);
do {
i = fin.read();
if(i != -1) fout.write(i);
} while(i != -1);
} Indian Institute of Information TechnologyKottayam 10
catch(IOException e) {
System.out.println("I/O Error: " + e);
} finally{
try {
if(fin != null) fin.close();
} catch(IOException e2) {
System.out.println("Error Closing Input File");
}
try {
if(fout != null) fout.close();
} catch(IOException e2) {
System.out.println("Error Closing Output File");
}
}
}
}
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Various types of File Operations in Java

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