File operations

Variables stored in RAM vanish as soon as a program terminates or power is lost. To achieve data persistence, computer systems store information in secondary storage (SSDs, hard drives) as files.

Every file operation follows a strict four-stage lifecycle:

1. Open: The program requests a file handle from the operating system, specifying the path and the mode of operation.
2. Read or Write: The program reads lines sequentially into memory or writes formatted text into buffer streams.
3. Flush / Handle Exceptions: Any I/O errors (such as disk full or permissions denied) must be intercepted using exception handling.
4. Close: The file stream is closed, flushing all remaining cached data onto disk and releasing OS locks.

• Read mode ("r"): Opens an existing file. If the file is missing, a FileNotFoundException is thrown. The file pointer starts at byte 0.
• Write mode ("w"): Creates a new file. If a file with that name already exists, its contents are permanently erased (truncated) without warning.
• Append mode ("a"): Opens a file with the write pointer positioned at the very end, allowing new records to be added without modifying existing data.

Comma-Separated Values (CSV) files store tabular records as plain text lines separated by commas. Processing CSV files combines file reading with string manipulation:

// Reading and parsing CSV lines
while file.hasNextLine()
    line = file.readLine()
    fields = line.split(",") // Array of comma-delimited tokens
    name = fields[0]
    score = parseInt(fields[1])
    process(name, score)
end while