Java Input Output

Java I/O

Java I/O (Input and Output) is used to process the input and produce the output.

Java uses the concept of a stream to make I/O operation fast. The java.io package contains all the
classes required for input and output operations.

We can perform file handling in Java by Java I/O API.

Stream

A stream is a sequence of data. In Java, a stream is composed of bytes. It's called a stream because it
is like a stream of water that continues to flow.

In Java, 3 streams are created for us automatically. All these streams are attached with the console.

 System.out: standard output stream

 System.in: standard input stream

 System.err: standard error stream


Code to print output and an error message to the console.

 System.out.println("simple message");

 System.err.println("error message");


Code to get input from console.

int i=System.in.read();//returns ASCII code of 1st character

System.out.println((char)i);//will print the character

OutputStream vs InputStream

OutputStream

 Java application uses an output stream to write data to a destination; it may be a file, an
array, peripheral device or socket.

InputStream

 Java application uses an input stream to read data from a source; it may be a file, an array,
peripheral device or socket.

Working of Java OutputStream and InputStream by the figure given below.




1

,OutputStream class

OutputStream class is an abstract class. It is the superclass of all classes representing an output
stream of bytes. An output stream accepts output bytes and sends them to some sink.

Useful methods of OutputStream


Method Description


1) public void write(int)throws IOException is used to write a byte to the current output stream.


2) public void write(byte[])throws is used to write an array of byte to the current output
IOException stream.


3) public void flush()throws IOException flushes the current output stream.


4) public void close()throws IOException is used to close the current output stream.




OutputStream Hierarchy




2

,InputStream class

InputStream class is an abstract class. It is the superclass of all classes representing an input stream
of bytes.

Useful methods of InputStream


Method Description


public abstract int read()throws reads the next byte of data from the input stream. It returns -1
IOException at the end of the file.


public int available()throws returns an estimate of the number of bytes that can be read
IOException from the current input stream.


public void close()throws is used to close the current input stream.
IOException




InputStream Hierarchy




Java FileOutputStream Class

Java FileOutputStream is an output stream used for writing data to a file.

If you have to write primitive values into a file, use FileOutputStream class. You can write byte-
oriented as well as character-oriented data through FileOutputStream class. But, for character-
oriented data, it is preferred to use FileWriter than FileOutputStream.

FileOutputStream class declaration

Declaration for Java.io.FileOutputStream class:

3

, public class FileOutputStream extends OutputStream

FileOutputStream class methods


Method Description


protected void finalize() It is used to clean up the connection with the file output stream.


void write(byte[] ary) It is used to write ary.length bytes from the byte array to the file
output stream.


void write(byte[] ary, int off, It is used to write len bytes from the byte array starting at offset off to
int len) the file output stream.


void write(int b) It is used to write the specified byte to the file output stream.


FileChannel getChannel() It is used to return the file channel object associated with the file
output stream.


FileDescriptor getFD() It is used to return the file descriptor associated with the stream.


void close() It is used to closes the file output stream.




Java FileOutputStream

Example 1: write byte

import java.io.FileOutputStream;

public class FileOutputStreamExample {

public static void main(String args[]){

try{

FileOutputStream fout=new FileOutputStream("D:\\testout.txt");

fout.write(65);

fout.close();

System.out.println("success...");



4