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 Java. 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 Java 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 (note the use of a single backslash in Java string literals, as special characters such as \ are escaped with an extra \)

• 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 Java:

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1String filePath = "input.txt";  // Relative path

Ensure your Java 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 Java, it's important to understand your directory structure. Here are a few examples with file trees:

1. Example 1:

   File Tree:

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   1project/
   2├── program
   3└── data/
   4    └── input.txt

   Relative Path:

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   1String filePath = "data/input.txt";

2. Example 2:

   File Tree:

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   1user/
   2├── documents/
   3│   └── program
   4└── input.txt

   Relative Path:

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   1String filePath = "../input.txt";

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

3. Example 3:

   File Tree:

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   1application/
   2├── scripts/
   3│   ├── program1
   4│   └── program2
   5└── resources/
   6    └── input.txt

   Relative Path (assuming the program is in program2):

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   1String filePath = "../resources/input.txt";

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.get() in Java. This method 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.get() 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: Path 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 the java.nio.file package, 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.get() to obtain a Path object:

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1import java.io.IOException;
2import java.nio.file.Path;
3import java.nio.file.Paths;
4
5public class Main {
6    public static void main(String[] args) throws IOException {
7        // Create a Path object for the specified file
8        Path filePath = Paths.get("example.txt");
9    }
10}

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

In Java, the Files class, along with the Paths class from java.nio.file, provides methods to handle file input. To open and read a file, you use the readString method. Here is how you can use it:

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1import java.io.IOException;
2import java.nio.file.Files;
3import java.nio.file.Path;
4import java.nio.file.Paths;
5
6public class Main {
7    public static void main(String[] args) throws IOException {
8        // Create a Path object for the specified file
9        Path filePath = Paths.get("example.txt");
10
11        // Read the entire file content into a string
12        String content = Files.readString(filePath);
13    }
14}

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

To display the contents of a file in Java, 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:

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1import java.io.IOException;
2import java.nio.file.Files;
3import java.nio.file.Path;
4import java.nio.file.Paths;
5
6public class Main {
7    public static void main(String[] args) throws IOException {
8        // Create a Path object for the specified file
9        Path filePath = Paths.get("example.txt");
10
11        // Read the entire file content into a string
12        String content = Files.readString(filePath);
13        
14        // Display the file's contents
15        System.out.println("Full file content:");
16        System.out.println(content);
17    }
18}

In this snippet, the content variable, which contains the entire file's contents, is printed using System.out.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 Java.
• Utilize Java's Files and Paths classes to open a file and manage the data through the 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 Java in the future. Keep up the great work and happy coding!