Welcome to the first lesson in our course on "Fundamentals of Text Data Manipulation." This lesson will introduce you to the essential task of reading text files in Kotlin. Text files serve as a fundamental data source in programming, often used for storing data, configuration files, and logs. Being able to open and read files in Kotlin is a foundational skill you'll often rely on when working with data. By the end of this lesson, you will be able to read the entire contents of a text file into a string using Java's Files.readString method, facilitated by the Paths class, a crucial capability for various data manipulation tasks. Let's get started!

A file path is an address that indicates where a file is located in your system's storage. This path guides your program on where to find or save a file. There are two types of file paths commonly used:

• Absolute Path: This is the complete path to a file, starting from the root directory. Here are examples across different operating systems:

  • Linux: /home/user/documents/input.txt
  • macOS: /Users/user/documents/input.txt
  • Windows: C:\Users\user\documents\input.txt

• Relative Path: This path is relative to the directory in which your application is currently executing. For example, documents/input.txt assumes your executable is running from the user directory in these examples.

Here's how you can specify a file path in Kotlin:

Ensure your Kotlin program and the text file are in the same directory if using a relative path. Otherwise, consider using the absolute path to ensure your program can locate your file correctly.

When working with relative paths in Kotlin, it's important to understand your directory structure. Here are a few examples with file trees:

1. Example 1:

   File Tree:

   Relative Path:

2. Example 2:

   File Tree:

   Relative Path:

   The .. indicates moving up to the parent directory. This approach works similarly across platforms like macOS/Linux and Windows.

3. Example 3:

   File Tree:

   Relative Path (works for both program2 and program1):

These examples demonstrate how relative paths are determined by the program's current working directory.

Before we delve into reading a file's contents, it's essential to understand why we use Paths in Kotlin. This class provides a straightforward and efficient way to work with file paths by returning a Path object. Here's why it's beneficial:

1. Cross-Platform Compatibility: Using Paths ensures that paths are correctly formatted for the operating system you're working on, whether it's Windows, macOS, or Linux. It abstracts away the differences in file system path structures.

2. Safety and Robustness: A Path object offers a more reliable way to manage file paths compared to raw string manipulation. This decreases the chances of encountering issues with improperly formatted paths.

3. Path Manipulation: Paths provides methods for resolving paths, normalizing them, converting them to absolute paths, and more. This functionality is important for maintaining clean, efficient file management in applications.

4. Seamless Integration: Path objects work seamlessly with Java's file handling functions, facilitating various file operations like reading, writing, and copying files. This integration simplifies file I/O tasks and improves code readability.

Here is a basic example of how to use Paths to obtain a Path object in Kotlin:

In this snippet, Paths.get("example.txt") creates a object representing the file path to . This object can then be used in file operations, making the code more robust and easier to manage.

Kotlin supports both Java and Kotlin imports, enabling the use of classes and functions from both ecosystems.

Java Imports:

Pros:

• Interoperability: Use Java libraries seamlessly.
• Extensive Libraries: Access a wide range of Java libraries.

Cons:

• Verbosity: More verbose than Kotlin.
• Null Safety: Requires explicit null handling.

Kotlin Imports:

Pros:

• Conciseness: Reduces boilerplate.
• Null Safety: Built-in null safety.

Cons:

• Learning Curve: New patterns for Java developers.
• Library Maturity: Smaller ecosystem than Java.

In Kotlin, the Files.readString method provides a straightforward way to handle file input. To open and read a file, you use the Files.readString method. Here is how you can use it:

In this snippet, Files.readString reads the entire content of the specified file into a string variable, content.

To display the contents of a file in Kotlin, after you have read the file's contents into a string variable using the Files.readString method, you can simply print the string to the console:

In this snippet, the content variable, which contains the entire file's contents, is printed using println, allowing you to view all the data stored in the file.

In this lesson, you've learned how to:

• Correctly specify file paths with examples from different operating systems using Kotlin.
• Utilize Java's Paths class to open a file and manage the data through the Files.readString method.
• Read the entire contents of a file from disk into a string variable.

These fundamental skills are crucial for handling data stored in text files. As you proceed to the practice exercises, you will apply these concepts by reading and extracting content from different text files. This hands-on practice will reinforce your understanding and prepare you for more advanced file manipulation techniques in Kotlin in the future. Keep up the great work and happy coding!