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:

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.

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.

 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..."); 
 } 
 }