Welcome to this lesson on reading files with FileReader in Java. Building upon our foundational knowledge of handling text files, this lesson will guide you through utilizing Java's java.io.FileReader to read files character by character. These methods are crucial for handling varying file sizes efficiently and managing memory use effectively. By the end of this lesson, you'll be able to read entire files, specific portions, and process files in manageable chunks, granting you flexible control over text data processing.

Before we jump into reading files, let's review the example file that we will work with:

This file contains multiple lines of varied lengths.

The FileReader class in Java is part of the java.io package and is designed for reading files as a stream of characters. It provides methods to open a file and read its contents character by character, which is helpful for detailed text processing. To read a file's entire content character by character, we open the file using FileReader and utilize the read() method, which reads the next character in the stream and returns its integer representation.

Here is how to read a file completely character by character using a loop:

To open the file, filePath.toFile() converts the Path object into a File object required by FileReader. The read() method reads a character from the file and returns its integer representation, which is then cast back to a character using (char). The loop continues until all characters have been read. It is crucial to close the FileReader after the operations to release system resources and prevent potential file locks.

The expected output is:

This approach suits situations where processing files one character at a time is necessary or preferred. It provides a straightforward way to read entire files while maintaining resource efficiency, making FileReader a versatile option for file manipulation in Java.

In many situations, you may only need to read a specific number of characters rather than the entire file. This can be accomplished by utilizing read() inside a loop that iterates a set number of times based on the count of characters you'd like to read.

The loop continues until the specified number of characters (in this case, 10) is read or until the end of the file is reached, whichever comes first.

The expected output is:

This method is especially useful for preliminary processing or debugging large files.

Sequential reading in file handling refers to the process of reading a file's contents in a predefined, orderly manner — part by part — without restarting from the beginning each time. For instance, by using loops in combination with the read() method, each subsequent read operation continues from where the last one concluded. This approach is particularly beneficial when dealing with large files or when you require distinct segments from a file.

Here's an example:

This program reads and prints the first 10 characters from the file, then moves forward to read the next set of 10 characters. The FileReader maintains its position within the file, allowing seamless sequential access to subsequent portions.

Expected output would be:

This technique is advantageous when you only need specific sections of a file or when you want to process large files in smaller chunks, thereby reducing memory consumption and improving performance. It facilitates better data manipulation in scenarios where progressive reading is required.

In this lesson, you learned how to effectively use the Java FileReader class for various file reading tasks. We covered reading entire files, specific portions, and processing large files efficiently by chunk reading. These techniques provide you with control and flexibility in handling text data.

Experiment with these methods using different files to strengthen your understanding of file manipulation in Java. Keep practicing to enhance your skills in file handling and data processing. You have made substantial progress in mastering file manipulation in Java.