JAVA_Chapter5_USING I/O

5.1 Console and File I/O

I/O

I/O stands for Input and Output.

• Input → data taken from user/file
• Output → data displayed or stored

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Types of I/O

Type	Description
Console I/O	keyboard and monitor interaction
File I/O	reading/writing files

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Console Output

println()

System.out.println("Hello");

Prints with newline.

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print()

System.out.print("Hello");

Prints without newline.

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printf()

System.out.printf("%d",10);

Formatted output.

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Console Input Using Scanner

import java.util.Scanner;

class Test{

   public static void main(String args[]){

      Scanner sc =
      new Scanner(System.in);

      int x = sc.nextInt();

      System.out.println(x);
   }
}

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Scanner Class Methods

Method	Purpose
nextInt()	integer input
nextFloat()	float input
nextDouble()	double input
next()	single word string
nextLine()	full line input
nextBoolean()	boolean input

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5.2 Opening and Closing Files

File

A file is a collection of data stored permanently.

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Opening File

FileReader fr =
new FileReader("a.txt");

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Closing File

fr.close();

Important to release resources.

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Creating File Object

import java.io.*;

File f = new File("a.txt");

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Useful File Methods

Method	Purpose
exists()	checks file existence
createNewFile()	creates file
delete()	deletes file
length()	returns file size
getName()	returns filename

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Example

import java.io.*;

class Test{

   public static void main(String args[])
   throws Exception{

      File f = new File("abc.txt");

      if(f.exists()){

         System.out.println("File Exists");
      }
   }
}

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5.3 Scanner Class

Definition

Scanner class is used to take input from keyboard or file.

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Importing Scanner

import java.util.Scanner;

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Scanner from Keyboard

Scanner sc =
new Scanner(System.in);

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Scanner from File

Scanner sc =
new Scanner(new File("a.txt"));

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Complete Scanner Example

import java.util.Scanner;

class Test{

   public static void main(String args[]){

      Scanner sc =
      new Scanner(System.in);

      String name =
      sc.nextLine();

      int age =
      sc.nextInt();

      System.out.println(name);
      System.out.println(age);
   }
}

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5.4 Byte Streams and Character Streams

Stream

A stream is a flow of data.

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Types of Streams

Type	Used For
Byte Stream	binary data
Character Stream	text data

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Byte Stream Classes

• FileInputStream
• FileOutputStream
• BufferedInputStream
• BufferedOutputStream

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Character Stream Classes

• FileReader
• FileWriter
• BufferedReader
• BufferedWriter

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Difference Between Byte Stream and Character Stream

Byte Stream	Character Stream
handles binary data	handles text data
8-bit	16-bit Unicode
InputStream/OutputStream	Reader/Writer

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5.5 Reading and Writing Byte Streams

FileOutputStream

Used to write byte data into file.

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Writing Byte Stream

import java.io.*;

class Test{

   public static void main(String args[])
   throws Exception{

      FileOutputStream fout =
      new FileOutputStream("a.txt");

      String s = "Hello";

      byte b[] = s.getBytes();

      fout.write(b);

      fout.close();

      System.out.println("Written");
   }
}

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FileInputStream

Used to read byte data from file.

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Reading Byte Stream

import java.io.*;

class Test{

   public static void main(String args[])
   throws Exception{

      FileInputStream fin =
      new FileInputStream("a.txt");

      int i;

      while((i=fin.read())!=-1){

         System.out.print((char)i);
      }

      fin.close();
   }
}

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5.6 Reading and Writing Character Streams

FileWriter

Used to write character data.

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Writing Character Stream

import java.io.*;

class Test{

   public static void main(String args[])
   throws Exception{

      FileWriter fw =
      new FileWriter("a.txt");

      fw.write("Hello Java");

      fw.close();
   }
}

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FileReader

Used to read character data.

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Reading Character Stream

import java.io.*;

class Test{

   public static void main(String args[])
   throws Exception{

      FileReader fr =
      new FileReader("a.txt");

      int i;

      while((i=fr.read())!=-1){

         System.out.print((char)i);
      }

      fr.close();
   }
}

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BufferedReader

Used for efficient reading.

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BufferedReader Example

import java.io.*;

class Test{

   public static void main(String args[])
   throws Exception{

      BufferedReader br =
      new BufferedReader(
      new InputStreamReader(System.in));

      String s = br.readLine();

      System.out.println(s);
   }
}

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BufferedWriter Example

import java.io.*;

class Test{

   public static void main(String args[])
   throws Exception{

      BufferedWriter bw =
      new BufferedWriter(
      new FileWriter("a.txt"));

      bw.write("Hello");

      bw.close();
   }
}

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5.7 Random Access Files

RandomAccessFile

Used to access file at any position.

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Syntax

RandomAccessFile f =
new RandomAccessFile(
"a.txt","rw");

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Modes

Mode	Meaning
r	read only
rw	read and write

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Writing Using RandomAccessFile

import java.io.*;

class Test{

   public static void main(String args[])
   throws Exception{

      RandomAccessFile f =
      new RandomAccessFile(
      "a.txt","rw");

      f.writeBytes("Hello");

      f.close();
   }
}

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Reading Using RandomAccessFile

import java.io.*;

class Test{

   public static void main(String args[])
   throws Exception{

      RandomAccessFile f =
      new RandomAccessFile(
      "a.txt","r");

      String s = f.readLine();

      System.out.println(s);

      f.close();
   }
}

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seek() Method

Moves pointer position.

f.seek(5);

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Advantages of RandomAccessFile

• Direct access
• Fast modification
• Efficient for large files

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Important I/O Classes

Class	Purpose
Scanner	input
File	file operations
FileReader	read text file
FileWriter	write text file
FileInputStream	read byte file
FileOutputStream	write byte file
BufferedReader	efficient reading
BufferedWriter	efficient writing
RandomAccessFile	random file access

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Most Important Practical Programs

1. Scanner input program
2. File creation program
3. FileReader program
4. FileWriter program
5. FileInputStream program
6. FileOutputStream program
7. BufferedReader program
8. BufferedWriter program
9. RandomAccessFile program
10. seek() method program

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Most Important Theory Questions

• What is I/O?
• Difference between byte stream and character stream.
• Explain Scanner class.
• Explain FileReader and FileWriter.
• Explain FileInputStream and FileOutputStream.
• Explain BufferedReader.
• What is RandomAccessFile?
• Explain seek() method.
• Difference between console I/O and file I/O.

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Important Viva Questions

Which class is used for keyboard input?

Scanner

Which package contains I/O classes?

java.io

Which stream is used for text data?

Character stream.

Which stream is used for binary data?

Byte stream.

Which class is used for random file access?

RandomAccessFile

Which method closes file?

close()

Which method moves file pointer?

seek()