All IT Courses 50% Off

Reading and Writing text file in Java
  1. Introduction to Reading a text File in Java:
  • There are many ways to read a plain text file in Java.
  • We are using FileReader, BufferedReader, and Scanner to read a text file.
  • This utility provides something special like:
    • BufferedReader: It provides buffering of data for fast reading.
    • Scanner: It provides parsing ability.

A. BufferedReader:

  • The BufferReader reads the text from a character-input stream.
  • It also did buffering for the reading of the characters, arrays, and the lines.

Let's have an Example:

BufferedReader in = new BufferedReader(Reader in, int size);

Program: 

import java.io.*;  public class ReadFile {   public static void main(String[] arg)throws Exception   {     File fi = new File("C:\\Users\\read\\Desktop\\test.txt");     BufferedReader br = new BufferedReader(new FileReader(fi));     String st;   while ((st = br.readLine()) != null)   System.out.println(st);   }  }

B. FileReader Class: It is a class for reading character files.

import java.io.*;  public class ReadingFile  {   public static void main(String[] arg) throws Exception   {   FileReader fileread= new FileReader("C:\\Users\\test\\Desktop\\test.txt");     int i;   while ((i=fileread.read()) != -1)   System.out.print((char) i);   }  }

C. Scanner Class:

  • A scanner which can parse the primitive types and also using strings through regular expressions.
  • A Scanner class can break its input into tokens, which by default matches whitespace.
  • These resulting tokens may then be converted into values of different types using the various next methods. 
// Java Program to illustrate reading from Text File  // using Scanner Class  import java.io.File;  import java.util.Scanner;  public class ReadFromFileUsingScanner  {   public static void main(String[] arg) throws Exception   {   // pass the path to the file as a parameter   File file = new File("C:\\Users\\test\\Desktop\\test.txt");   Scanner sc = new Scanner(file);     while (sc.hasNextLine())   System.out.println(sc.nextLine());   }  }

2. Introduction to Writing a text File in Java:

a. Java BufferedWriter Class:

  • Java BufferedWriter class is used to provide buffering for Writer instances.
  • It makes the performance fast.
  • It inherits the Writer class.
  • The buffering characters are used for delivering the efficient writing of single arrays, characters, and strings.
  • Creates a buffered character-output stream that uses a default-sized output buffer.

public class BufferedWriter extends Writer

Program: 

import java.io.*;  public class NewClass  {   public static void main(String[] args)   {   //initializing FileWriter   FileWriter filewrite;   try  {  filewrite = new FileWriter("ABC.txt");     // Initialing BufferedWriter   BufferedWriter bufferwrite = new BufferedWriter(filewrite);   System.out.println("Buffered Writer start writing :)");     // Use of write() method to write the value in 'ABC' file   bufferwrite.write(69);   bufferwrite.write(49);     // Closing BufferWriter to end operation   bufferwrite.close();   System.out.println("Written successfully");   }   catch (IOException excpt)   {   excpt.printStackTrace();   }     }  }

b) Java FileWriter Class

  • This class is used to write character-oriented data to a file.
  • It is a character-oriented class which is used for file handling in java.
  • Unlike the FileOutputStream class, you don't need to convert the string into a byte array because it provides a method to write string directly.

public class FileWriter extends OutputStreamWriter

Program: 

              import java.io.FileWriter;   public class FileWriterExample {   public static void main(String args[]){   try{   FileWriter fw=new FileWriter("D:\\testout.txt");   fw.write("Welcome");   fw.close();   } catch(Exception e) { System.out.println(e); }   System.out.println("Success...");   }   }
Learn Java Online