Java program reads the content of files line by line

Comprehensive Java Examples

In this example, we will learn how to use various classes in Java to read the content of files.

To understand this example, you should understand the followingJava programmingTopic:

• Java file class

• Java BufferedInputStream class

• Java FileReader class

Example1: Java program uses BufferedInputStream to read files

import java.io.BufferedInputStream;
import java.io.FileInputStream;
class Main {
　　public static void main(String[] args) {
　　　　try {
　　　　　　//Create FileInputStream
　　　　　　FileInputStream file = new FileInputStream("input.txt");
　　　　　　//Create BufferedInputStream
　　　　　　BufferedInputStream input = new BufferedInputStream(file);
　　　　　　//Read the first byte from the file
　　　　　　int i = input.read();
　　　　　　while (i !=　-1) {
　　　　　　　　System.out.print((char) i);
　　　　　　　　//　Read the next byte from the file
　　　　　　　　i = input.read();
　　　　　　}
　　　　　　input.close();
　　　　}
　　　　catch (Exception e) {
　　　　　　e.getStackTrace();
　　　　}
　　}
}

Output Result

First Line
Second Line
Third Line
Fourth Line
Fifth Line

In the above example, we use BufferedInputStreamClass from the file namedinput.txtRead the file line by line.

NoteTo run this file, you should have a file named input.txt in the current working directory.

Example2A Java program using BufferedReader to read files

import java.io.FileReader;
import java.io.BufferedReader;
class Main {
　　public static void main(String[] args) {
　　　　//Create a character array
　　　　char[] array = new char[100];
　　　　try {
　　　　　　//　Create a FileReader
　　　　　　FileReader file = new FileReader("input.txt");
　　　　　　//Create BufferedReader
　　　　　　BufferedReader input = new BufferedReader(file);
　　　　　　//Read characters
　　　　　　input.read(array);
　　　　　　System.out.println("Data in the file: ");
　　　　　　System.out.println(array);
　　　　　　//Close the reader
　　　　　　input.close();
　　　　}
　　　　catch(Exception e) {
　　　　　　e.getStackTrace();
　　　　}
　　}
}

Output Result

Data in the file:　
First Line
Second Line
Third Line
Fourth Line
Fifth Line

In the above example, we useBufferedReader classRead the file namedinput.txtof the file.

Example3A Java program to read files using a scanner

import java.io.File;
import java.util.Scanner;
class Main {
　　public static void main(String[] args) {
　　　　try {
　　　　　　//Create a new file object
　　　　　　File file = new File("input.txt");
　　　　　　//Create a scanner object associated with the file
　　　　　　Scanner sc = new Scanner(file);
　　　　　　//Read each line in the file and print it out
　　　　　　System.out.println("Use a scanner to read the file:");
　　　　　　while(sc.hasNextLine()) {
　　　　　　　　System.out.println(sc.nextLine());
　　　　　　}
　　　　　　//Close the scanner
　　　　　　sc.close();
　　　　} catch (Exception e) {
　　　　　　e.getStackTrace();
　　　　}
　　}
}

Output Result

Read the file using the scanner:
First Line
Second Line
Third Line
Fourth Line
Fifth Line

In the above example, we created an object of the File class named file. Then, we created a Scanner object associated with the file.

Here, we use scanner methods

• hasNextLine() - Returns true if the next line exists in the file

• nextLine() - Return a whole line from the file

For more information about the scanner, please visitJava Scanner.

Comprehensive Java Examples