Welcome to another lesson, where we'll delve into the essential technique of reading files line-by-line using Java's Files and Paths classes. In many practical applications, especially those involving large files such as logs or continuous data streams, processing data one line at a time is crucial for efficient data management. By the end of this lesson, you'll learn how to effectively read and process file data line-by-line using Java.
To read a file line-by-line in Java, you can use the Files.readAllLines method to read the lines into a List<String>, and then iterate over the list using a for-each loop. Let's see this in action:
Java1import java.io.IOException; 2import java.nio.file.Files; 3import java.nio.file.Path; 4import java.nio.file.Paths; 5import java.util.List; 6 7public class Main { 8 public static void main(String[] args) throws IOException { 9 // Create a Path object for the specified file 10 Path filePath = Paths.get("example.txt"); 11 12 // Read all lines from the file into a list 13 List<String> lines = Files.readAllLines(filePath); 14 15 // Iterate through each line and output it 16 for (String line : lines) { 17 System.out.println(line); 18 } 19 } 20}
Here, Files.readAllLines(filePath) reads lines from data.txt and stores them in a list. Each line is then printed to the console.
Imagine needing to process a set of numbers stored in a file — reading each integer and calculating their sum. This is a practical task you can easily accomplish using Files.readAllLines and basic string manipulation in Java.
Assume numbers.txt contains:
Plain text110 220 330 440
The following code reads integers from this file and calculates their sum:
Java1import java.io.IOException; 2import java.nio.file.Files; 3import java.nio.file.Path; 4import java.nio.file.Paths; 5import java.util.List; 6 7public class Main { 8 public static void main(String[] args) throws IOException { 9 // Create a Path object for the specified file 10 Path filePath = Paths.get("numbers.txt"); 11 // Read all lines into a list 12 List<String> lines = Files.readAllLines(Paths.get(filePath)); 13 // Initialize the variable to hold the sum of integers from the file 14 int totalSum = 0; 15 16 // Iterate through each line, convert to integer, and add to totalSum 17 for (String line : lines) { 18 try { 19 int number = Integer.parseInt(line); 20 totalSum += number; // Add the integer to totalSum 21 } catch (NumberFormatException e) { 22 System.out.println("Invalid number format in line: " + line); 23 } 24 } 25 // Display the total sum 26 System.out.println("The sum of the numbers is: " + totalSum); 27 } 28}
- Reading Numbers: Each line is parsed to an integer using
Integer.parseInt(), which safely converts strings to integers. - Calculating Sum: The integers are added together in the
totalSumvariable.
After running this code, it will display the total sum of the numbers:
Plain text1The sum of the numbers is: 100
In this lesson, you've developed the skills to read a text file line-by-line using Java — a crucial technique for processing large datasets efficiently. You've learned to manage file I/O operations with Files and Paths, and effectively handle each line of text data. You're now well-prepared to tackle practice exercises applying these concepts and further explore parsing techniques in upcoming lessons. Continue building on these skills and enjoy the journey!
