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Java Program to Read a Large Text File Line by Line

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As we are well verse with this topic let us put more stress in order to figure out minute differences between them. Here we are supposed to read from a file on the local directory where a text file is present say it be ‘gfg.txt’. Let the content inside the file be as shown below:

Geeks for Geeks.
A computer science portal.
Welcome to this portal.
Hello Geek !!!

Note: Keep a check that prior doing anything first create a file on the system repository to deal with our program\writing a program as we will be accessing the same directory through our programs.

Methods:

  1. Using Scanner class
  2. Using BufferedReaader class

Method 1: Using Scanner class

Scanner is a class in java.util package used for obtaining the input of the primitive types like int, double, etc. and strings. It is the easiest way to read input in a Java program, though not very efficient if you want an input method for scenarios where time is a constraint like in competitive programming. Scanner class is used to read the large file line by line. A Scanner breaks its input into tokens, which  by default matches the whitespace. 

Example

Java




// Java Program to Read a Large Text File Line by Line
// Using Scanner class
 
// Importing required classes
import java.io.*;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.InputStream;
import java.nio.charset.StandardCharsets;
import java.util.Scanner;
 
// Main class
public class GFG {
 
    // Main driver method
    public static void main(String[] args)
        throws FileNotFoundException
    {
 
        // Declaring and initializing the string with
        // custom path of a file
        String path = "C:\\Users\\HP\\Desktop\\gfg.txt";
 
        // Creating an instance of Inputstream
        InputStream is = new FileInputStream(path);
 
        // Try block to check for exceptions
        try (Scanner sc = new Scanner(
                 is, StandardCharsets.UTF_8.name())) {
 
            // It holds true till there is single element
            // left in the object with usage of hasNext()
            // method
            while (sc.hasNextLine()) {
 
                // Printing the content of file
                System.out.println(sc.nextLine());
            }
        }
    }
}


Output: 

Geeks for Geeks.
A computer science portal.
Welcome to this portal.
Hello Geek !!!

Method 2: Using BufferedReader class

BufferedReader is used to read the file line by line. Basically, BufferedReader() is used for the processing of large files. BufferedReader is very efficient for reading. 

Note: Specify the size of the BufferReader or keep that size as a Default size of BufferReader. The default size of BufferReader is 8KB. 

Syntax:

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

Example:

Java




// Java Program to Read a Large Text File Line by Line
// Using BufferedReader class
 
// Importing required classes
import java.io.*;
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
 
// Main class
public class GFG {
 
    // Main driver method
    public static void main(String[] args)
    {
 
        // Declaring a string and initializing it with
        // path of file present on the system
        String path = "C:\\Users\\HP\\Desktop\\gfg.txt";
 
        // Try block to check for exceptions
        try (BufferedReader br
             = new BufferedReader(new FileReader(path))) {
 
            // Declaring a new string
            String str;
 
            // It holds true till threre is content in file
            while ((str = br.readLine()) != null) {
 
                // Printing the file data
                System.out.println(br);
            }
        }
 
        // Catch block to handle the exceptions
        catch (IOException e) {
 
            // Display pop up message if exceptionn occurs
            System.out.println(
                "Error while reading a file.");
        }
    }
}


Output: 

Geeks for Geeks.
A computer science portal.
Welcome to this portal.
Hello Geek !!!


Last Updated : 26 Aug, 2022
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