InputStreamReader class in Java

An InputStreamReader is a bridge from byte streams to character streams. It reads bytes and decodes them into characters using a specified charset. The charset that it uses may be specified by name or may be given explicitly, or the platform’s default charset may be accepted. 
Declaration :

public class InputStreamReader
   extends Reader

Constructors :

• InputStreamReader(InputStream in_strm) : Creates an InputStreamReader that uses the default charset.
• InputStreamReader(InputStream in_strm, Charset cs) : creates an InputStreamReader that uses the given charset.
• InputStreamReader(InputStream in_strm, CharsetDecoder dec) : Creates an InputStreamReader that uses the given charset decoder.
• InputStreamReader(InputStream in_strm, String charsetName) : Creates an InputStreamReader that uses the named charset

Methods: 

• ready() : java.io.InputStreamReader.ready() tells whether the Character stream is ready to be read or not. An InputStreamReader is ready if its input buffer is not empty, or if bytes are available to be read from the underlying byte stream. 
  Syntax : 

public boolean ready()
Returns :
True : if the Character stream is ready to be read
False : if the Character stream is not ready to be read

• close() : java.io.InputStreamReader.close() closes InputStreamReader and releases all the Streams associated with it. Once the stream has been closed, further read(), ready(), mark(), reset(), or skip() invocations will throw an IOException. 
  Syntax : 

public void close()
Returns :
No value is returned

• Implementation of ready() and close() method : 

Java

// Java program illustrating ready() and close() method

import java.io.*;
public class NewClass
{
    public static void main(String[] args)
    {

        try
        {
            // initializing FileInputStream
            FileInputStream geek = new FileInputStream("ABC.txt");

            // Initializing InputStreamReader object
            InputStreamReader in_strm = new InputStreamReader(geek);

            int t;
            while((t=in_strm.read())!= -1)
            {
                // convert the integer true to character
                char r = (char)t;
                System.out.println("Character : "+r);

                // check if the stream in_strm ready
                boolean b = in_strm.ready();
                // Use of ready() methods
                System.out.println("Ready? : "+b);

            }

            // Use of close() method to Close InputStreamReader
            in_strm.close();

            // Closing FileInputStream
            geek.close();
        }
        catch (FileNotFoundException fnfe)
        {
            System.out.println("NO Such File Exists");
        }
        catch (IOException except)
        {
            System.out.println("IOException occurred");
        }
    }
}

• Note : 
  All the programs in this article won’t run on online IDE as no ‘ABC’ file exists. You can check this code on Java compiler on your system. 
  To check this code, create a file ‘ABC’ on your system. 
  ‘ABC’ file contains : 
  Geeks 
  For 
  Geeks 
  Output : 

Character : G
Ready? : true
Character : e
Ready? : true
Character : e
Ready? : true
Character : k
Ready? : true
Character : s
Ready? : true
Character :  
Ready? : true
Character : 
Ready? : true
Character : 

Ready? : true
Character : F
Ready? : true
Character : o
Ready? : true
Character : r
Ready? : true
Character :  
Ready? : true
Character : 
Ready? : true
Character : 

Ready? : true
Character : G
Ready? : true
Character : e
Ready? : true
Character : e
Ready? : true
Character : k
Ready? : true
Character : s
Ready? : false

• getEncoding() : java.io.InputStreamReader.getEncoding() returns the name of the character encoding being used by this stream. 
  Syntax : 

public String getEncoding()
Parameters : 
Returns :
No value is returned

• Implementation of getEncoding() method : 

Java

// Java program illustrating getEncoding() method

import java.io.*;
public class NewClass
{
    public static void main(String[] args)
    {

        try
        {
            // initializing FileInputStream
            FileInputStream geek = new FileInputStream("ABC.txt");

            // Initializing InputStreamReader object
            InputStreamReader in_strm = new InputStreamReader(geek);

            // Use of getEncoding() method
            // to get the character encoding present in the stream
            String encoding = in_strm.getEncoding();

            System.out.println("Encoding used : "+encoding);

            // Closing InputStreamReader
            in_strm.close();

            // Closing FileInputStream
            geek.close();
        }
        catch (FileNotFoundException fnfe)
        {
            System.out.println("NO Such File Exists");
        }
        catch (IOException except)
        {
            System.out.println("IOException occurred");
        }
    }
}

• Output : 

Encoding used : UTF8

• read() : java.io.InputStreamReader.read() Returns single character after reading. 
  Syntax : 

public int read()
Returns :
Returns single character after reading or -1 if the end of the stream has been reached

• Implementation : 

Java

// Java program illustrating read() method

import java.io.*;
public class NewClass
{
    public static void main(String[] args) throws FileNotFoundException, IOException
    {

        // initializing FileInputStream
        FileInputStream geek = new FileInputStream("ABC.txt");

        // Initializing InputStreamReader object
        InputStreamReader in_strm = new InputStreamReader(geek);

        int t;
        String read_reslt="";

        // Use of read() method
        while((t = in_strm.read()) != -1)
        {
            read_reslt = read_reslt+(char)t;
        }

        // print the result read from the file
        System.out.println(read_reslt);
    }
}

• Note : 
  ‘ABC’ file contains : 
  1 
  Geeks 
  2 
  For 
  3 
  Geeks 
  Output : 

1
Geeks 
2
For 
3
Geeks