Welcome to this lesson on reading files with Kotlin. Building upon our foundational knowledge of handling text files in Kotlin, this lesson will guide you through reading files character by character using Kotlin's I/O operations. 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.

In Kotlin, reading a file character by character involves utilizing FileReader in conjunction with Kotlin's use construct for resource management. The FileReader allows us to open a file and read its contents one character at a time, which is helpful for detailed text processing. Here is how to read a file completely, character by character, using a loop:

With this approach, filePath.toFile() converts the Path object into a File object required by FileReader. The read() method reads a character from the file, returning its integer representation, which is then converted to a character using toChar(). The loop continues until all characters have been read. Using the use construct ensures that resources are closed automatically after operations, preventing potential file locks and freeing system resources.

The expected output is:

This technique is well-suited for situations where processing files one character at a time is necessary, providing an efficient way to manage resources during file manipulation in Kotlin.

In some 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 example, 10) is read or the end of the file is reached, whichever comes first. This method is especially useful for preliminary processing or debugging large files.

Expected output:

Sequential reading refers to reading a file's contents part by part in order, without restarting from the beginning each time. In Kotlin, this is managed seamlessly using loops and the read() method, allowing each subsequent read operation to continue from where the last one concluded. This is particularly beneficial for handling large files or when you require distinct segments from a file.

This program reads and prints the first 10 characters from the file, then moves forward to read the next set of 10 characters. Each reading segment stops either upon reaching the defined character length or upon encountering the end of the file signified by read() returning -1. By using the use construct, Kotlin continues maintaining its position within the file, supporting seamless sequential access to subsequent portions.

Expected output:

This technique is advantageous when you need specific sections of a file or want to process large files in smaller chunks, thus reducing memory consumption and improving performance.

While the use construct is an efficient way to manage resources in Kotlin, you can manually control the resource management by not using use. This requires explicitly closing the FileReader to prevent resource leaks. Below is an example of how this can be accomplished:

In this approach, the FileReader is explicitly closed in the finally block of a try-finally construct. This ensures that the file resource is released properly once you are done with it, similar to what the use construct does automatically. In practice, the use construct is preferable as it is more error-safe.

In this lesson, you learned how to effectively use Kotlin for various file reading tasks. We covered reading files character by character, extracting specific portions, and processing large files efficiently through sequential 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 Kotlin. Keep practicing to enhance your skills in file handling and data processing. You have made substantial progress in mastering file manipulation in Kotlin.