I/O

Class Reader

• It is an abstract class for reading character streams.
• Stream is a flow of data.
• By using reader we can read data from file or device or some remote system.

• int read()
• Reads a single character and returns it.
• For ex:
ch=dr.read();
• int read( char[] buffer )
• Reads characters into an array.
• Return no of chars actually read
• For ex:

            char arr[]=new char[100];
            int n=dr.read(arr);

• int read(char[] buffer, int offset, int len)
• Reads len chars and stores it into buffer at offset position.
• Return no of chars actually read.
• For ex:

            char arr[]=new char[100];
            int n=dr.read(arr,25,50);

Note:above read methods returns -1 at end of stream
• void close()
• Closes the stream and releases any system resources associated with it.

Class FileReader

• It is used for reading character files.
• It is derived from class Reader.

• FileReader(String fileName)
  • Creates a new FileReader, given the name of the file to read from.
  • For ex:
  FileReader dr=new FileReader("c:/temp/demo.txt");
• FileReader(File file)
• Creates a new FileReader, given the File to read from.
• For ex:

            File fa=new File("c:/temp/demo.txt");
            FileReader dr=new FileReader(fa);
        

 import java.io.*;
 class demo
 {
    public static void main(String[ ] args) throws Exception
   {
     	FileReader fd=new FileReader("c:\\temp\\info.txt");
	    int ch;
	    while((ch=fd.read())!=-1)
		    System.out.print((char)ch);
        fd.close();
   }
}

Welcome to CCIT
Amravati   

Class Writer

• Writer class is an abstract class.
• It is used to write to character streams.
• Stream mean flow of data By using Writer data may be send to a file or device or remote system

• void write(int c)
• It writes a single character.
• For ex:
wr.write('A');
• void write(String str)
• It writes a string.
• For ex:
wr.write("Amravati");
• void write(char[ ] cbuf)
• It writes an array of characters.
• For ex:

            char arr[]={'A','m','r','a','v','a','t','i'};
            wr.write(arr);

• void write(char[ ] cbuf, int offset, int len)
• It writes a portion of an array of characters.
• For ex:

            char arr[]={'A','m','r','a','v','a','t','i'};
            wr.write(arr,0,4);

• void write(char[ ] cbuf, int offset, int len)
• It writes a portion of an array of characterIt writes a portion of a string i.e. starting from offset and of len chars.
• For ex:

            String data="Amravati";
            wr.write(data,0,4);

Class FileWriter

• This class is used to write char data to a file.
• It is derived from class Writer

• FileWriter(String fileName)
  • Will create a FileWriter object to write data into file.
  • If file is present it will overwrite otherwise new file will be created.
  • For ex:
  FileWriter fw=new FileWriter("c:/temp/info.txt");
• FileWriter(File file)
• Will create a FileWriter object to write data into file.
• If file is present it will overwrite otherwise new file will be created.
• For ex:

            File fa=new File("c:/temp/info.txt");
            FileWriter fw=new FileWriter(fa);

• FileWriter(String fileName, boolean append)
• FileWriter(File file, boolean append)
• Will create a FileWriter object to write data into file.
• If append (true) is passed then data will be added at end.
• If append (false) is passed then file will be overwritten if present.

 import java.io.*;
 class demo
 {
    public static void main(String[ ] args) throws Exception
   {
     	FileWriter fw=new FileWriter("c:\\temp\\myinfo.txt");
	    fw.write("P.Choudhari");
	    fw.write("\nCCIT\nRajapeth\nAmravati");
	    fw.close();
   }
 }

 import java.io.*;
 class demo
 {
    public static void main(String[ ] args) throws Exception
   {
     	FileWriter fw=new FileWriter("c:\\temp\\myinfo.txt");
	    fw.write("P.Choudhari");
	    fw.write("\nCCIT\nRajapeth\nAmravati");
	    fw.close();
   }
 }

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