Lesson 1: Reading and Writing Files

Overview:

Lesson 1 Reading and Writing Files introduces the essential concepts of reading from and writing to files in Java. This includes working with streams, which are sequences of data elements made available over time. Understanding file I/O operations is crucial for handling external data and interacting with files in Java applications.

Key Concepts:

  1. File I/O in Java:
    • Reading from Files:
      • File Readers: Classes like FileReader and BufferedReader are used to read characters from a file.
      • File Streams: Streams like FileInputStream and BufferedInputStream can be used for reading binary data from a file.
    • Writing to Files:
      • File Writers: Classes like FileWriter and BufferedWriter are used to write characters to a file.
      • File Streams: Streams like FileOutputStream and BufferedOutputStream can be used for writing binary data to a file.
  2. Working with Streams:
    • Streams Overview: Streams are sequences of data elements made available over time. In Java, InputStream and OutputStream are the base classes for reading and writing binary data, while Reader and Writer are used for handling character data.
    • Buffering: Buffered streams, such as BufferedReader and BufferedWriter, enhance I/O performance by minimizing the number of interactions with the underlying file.

Example:

Let’s create a simple program that demonstrates reading from and writing to a text file in Java. We’ll use FileReader, BufferedReader, FileWriter, and BufferedWriter for file I/O operations.

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

public class FileIOExample {

    public static void main(String[] args) {
        // Writing to a file
        try (BufferedWriter writer = new BufferedWriter(new FileWriter("output.txt"))) {
            writer.write("Hello, Java! This is a file write example.");
        } catch (IOException e) {
            System.err.println("Error writing to file: " + e.getMessage());
        }

        // Reading from a file
        try (BufferedReader reader = new BufferedReader(new FileReader("output.txt"))) {
            String line;
            while ((line = reader.readLine()) != null) {
                System.out.println("Read from file: " + line);
            }
        } catch (IOException e) {
            System.err.println("Error reading from file: " + e.getMessage());
        }
    }
}

n this example, we use BufferedWriter to write a string to a file and BufferedReader to read the content of the file line by line. The try-with-resources statement is used to automatically close the resources (BufferedWriter and BufferedReader) after their usage, ensuring proper resource management. Understanding file I/O and streams is vital for interacting with external data and creating applications that handle data persistence.