File Handling in Java

• File input and output (I/O) operations in Java are crucial for reading from and writing to files.
• They are commonly used for tasks such as data persistence, file manipulation, and handling large datasets.
  • Reading from a File:
    1. We can read/fetch data from a file using various classes such as FileInputStream, BufferedReader, or Scanner.
    2. Here, the FileInputStream class contains read() & skip(), the BufferedReader class contains readLine(), and the Scanner class contains next(), nextLine(), nextInt(), etc.
    3. The FileInputStream class in Java is used for reading binary data from a file. It is a subclass of the InputStream class and provides methods for reading bytes from a file input stream. The read() method of the FileInputStream class reads the next byte of data from the input stream. It returns an int value representing the byte read, or -1 if the end of the file has been reached. Methods of FileInputStream throw IOException hence its handling is required. It’s important to close the FileInputStream object once we’re done reading from the file. This releases the file handle and any system resources associated with it.
  • Writing to a File:
    1. We can write/store data to a Java file using classes like FileOutputStream, BufferedWriter, or PrintWriter.
    2. Here, the FileOutputStream class contains write() & flush(), the BufferedWriter class contains write() & newLine(), and the PrintWriter class contains print(), println(), etc.
    3. In Java, the FileOutputStream class is used for writing binary data to a file. It’s a subclass of the OutputStream class and provides methods to write bytes to a file output stream. It’s typically used for writing binary data to files, such as images, videos, or any other non-textual data. The write(int b) method of the FileOutputStream class writes the specified byte to the output stream. The flush() method flushes the stream, ensuring that any buffered output bytes are written to the file. As with any resource, it’s important to close the FileOutputStream object once we’re done using it to release system resources. Methods of FileOutputStream can throw IOException if an I/O error occurs, such as the file not being found or the stream being closed.
    4. The PrintWriter class in Java provides methods to write formatted data to a file. It’s particularly useful when a user needs to write data in a human-readable format or when they want to easily concatenate text and data. It is an extension of the Writer class and offers several convenient methods for writing various data types as text representations. The PrintWriter is the class that provides various print(), and println() methods to write data of different types to the file. void print(String s) writes a string to the file without appending a newline character. void println(String s) writes a string to the file and appends a newline character. Similar methods exist for other data types like int, double, boolean, etc. The flush() method of the PrintWriter class flushes the stream, ensuring that any buffered output data is written to the file. As with any resource, it’s important to close the PrintWriter object once we’re done using it to release system resources. The methods of PrintWriter do not throw IOException.

File and Directory Navigation Operations:

• Listing Files in a Directory: The list() method returns an array of files and directories present in an existing directory.
• Navigating Directories: The File class provides methods like getParent() to get the parent directory, and listFiles() to retrieve all files present in a directory.