‍In the world of programming, the ability to read file contents line-by-line is a fundamental skill. Java, being one of the most popular programming languages, offers several methods to achieve this task efficiently. In this article, we will explore different approaches using Java classes such as java.io.BufferedReader, java.util.Scanner, Files.readAllLines(), and java.io.RandomAccessFile. Whether you are a beginner or an experienced developer, this comprehensive guide will equip you with the knowledge and proficiency needed to read file contents line-by-line in Java.

Table of Contents

1. Reading a File Line-by-Line using BufferedReader
2. Reading a File Line-by-Line using Scanner
3. Reading a File Line-by-Line using Files
4. Reading a File Line-by-Line using RandomAccessFile
5. Conclusion

Reading a File Line-by-Line using BufferedReader

One way to read a file line-by-line in Java is by using the java.io.BufferedReader class. This class provides the readLine() method, which allows us to read a file line-by-line as a String. When the end of the file is reached, the readLine() method returns null.

Here’s an example program that demonstrates how to read a file line-by-line using BufferedReader:

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class ReadFileLineByLineUsingBufferedReader {
public static void main(String[] args) {
BufferedReader reader;
try {
reader = new BufferedReader(new FileReader("sample.txt"));
String line = reader.readLine();
while (line != null) {
System.out.println(line);
line = reader.readLine();
}
reader.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}

The above program opens the file “sample.txt” using a BufferedReader and reads its contents line-by-line. Each line is printed to the console using System.out.println(). Finally, the BufferedReader is closed to release system resources.

Reading a File Line-by-Line using Scanner

Another approach to reading a file line-by-line in Java is by utilizing the java.util.Scanner class. With Scanner, we can open a file and read its contents line-by-line with ease.

Consider the following example program that demonstrates how to read a file line-by-line using Scanner:

import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;

public class ReadFileLineByLineUsingScanner {
public static void main(String[] args) {
try {
Scanner scanner = new Scanner(new File("sample.txt"));
while (scanner.hasNextLine()) {
System.out.println(scanner.nextLine());
}
scanner.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
}
}
}

In the above program, we create a Scanner object by passing the file “sample.txt” as an argument. The hasNextLine() method checks for the presence of the next line, and nextLine() reads and returns the line as a String. The loop continues until there are no more lines to read. Finally, the Scanner is closed to prevent any resource leaks.

Reading a File Line-by-Line using Files

The java.nio.file.Files class provides a convenient method called readAllLines() that enables us to read all the lines of a file into a list of strings. This approach simplifies the process of reading a file line-by-line in Java.

Here’s an example program that demonstrates how to read a file line-by-line using Files:

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.List;

public class ReadFileLineByLineUsingFiles {
public static void main(String[] args) {
try {
List<String> allLines = Files.readAllLines(Paths.get("sample.txt"));
for (String line : allLines) {
System.out.println(line);
}
} catch (IOException e) {
e.printStackTrace();
}
}
}

In the above program, we use the readAllLines() method from Files to read all the lines of the file “sample.txt” into the allLines list. We then iterate over the list using a for loop and print each line to the console.

Reading a File Line-by-Line using RandomAccessFile

The java.io.RandomAccessFile class provides a way to read a file line-by-line by opening the file in read mode and using its readLine() method. This approach offers flexibility when reading specific lines from a file.

Consider the following example program that demonstrates how to read a file line-by-line using RandomAccessFile:

import java.io.IOException;
import java.io.RandomAccessFile;

public class ReadFileLineByLineUsingRandomAccessFile {
public static void main(String[] args) {
try {
RandomAccessFile file = new RandomAccessFile("sample.txt", "r");
String line;
while ((line = file.readLine()) != null) {
System.out.println(line);
}
file.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}

In the above program, we create a RandomAccessFile object by passing the file “sample.txt” and the mode “r” (read mode) as arguments. The readLine() method reads and returns a line from the file, and the loop continues until there are no more lines to read. Finally, the RandomAccessFile is closed to free system resources.

Conclusion

In this article, we explored various ways to read file contents line-by-line in Java. We learned how to use the java.io.BufferedReader, java.util.Scanner, Files.readAllLines(), and java.io.RandomAccessFile classes to achieve this task efficiently. Whether you are working with large files or need to access specific lines, Java provides the necessary tools to handle file reading with ease. By mastering these techniques, you will be well equipped to manipulate file contents in your Java applications.

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Christian Wells