FileNotFoundException

Why This Happens

FileNotFoundException is thrown when trying to open a file that does not exist, the path is a directory rather than a file, or the file cannot be opened for the requested access. Relative paths resolve from the working directory, which may not be what you expect.

The Problem

FileReader reader = new FileReader("data.txt"); // File doesn't exist

The Fix

Path path = Path.of("data.txt");
if (Files.exists(path)) {
    try (BufferedReader reader = Files.newBufferedReader(path)) {
        String content = reader.readLine();
    }
} else {
    System.err.println("File not found: " + path.toAbsolutePath());
}

Step-by-Step Fix

1. 1

   Identify the file path

   Read the exception message for the exact path. Print the absolute path to see where Java is actually looking.

2. 2

   Verify the path

   Check that the file exists at that location, the name is spelled correctly, and the extension is right.

3. 3

   Fix the path or handle absence

   Use an absolute path, load from classpath with getResourceAsStream(), or check Files.exists() before opening.