Working with Files, Directories, and Streams in Java

1. Understanding Files and Directories

Files store data persistently on storage devices. Directories are used to organize files and may contain other directories, creating a hierarchical structure.

Example: Working with the File Class

File file = new File("example.txt");
System.out.println("File exists: " + file.exists());

// Creating a new file
if (file.createNewFile()) {
    System.out.println("File created successfully.");
}

// Deleting a file
if (file.delete()) {
    System.out.println("File deleted successfully.");
}

2. Byte vs Character Streams

Java I/O supports two types of streams:

• Byte Streams: Work with binary data. Classes include InputStream and OutputStream.
• Character Streams: Work with text data. Classes include Reader and Writer.

Byte Stream Example:

FileInputStream input = new FileInputStream("example.txt");
int data;
while ((data = input.read()) != -1) {
    System.out.print((char) data);
}
input.close();

Character Stream Example:

FileReader reader = new FileReader("example.txt");
int data;
while ((data = reader.read()) != -1) {
    System.out.print((char) data);
}
reader.close();

3. Low-Level vs High-Level Streams

Low-level streams operate directly on resources (e.g., files), while high-level streams filter or buffer data.

Example of Buffered Stream (High-Level):

BufferedReader bufferedReader = new BufferedReader(new FileReader("example.txt"));
String line;
while ((line = bufferedReader.readLine()) != null) {
    System.out.println(line);
}
bufferedReader.close();

4. Common Stream Classes

The following classes are essential for file and stream manipulation:

• BufferedReader / BufferedWriter
• FileInputStream / FileOutputStream
• FileReader / FileWriter
• ObjectInputStream / ObjectOutputStream
• PrintWriter

5. Common Stream Operations

Input and output streams include methods for common operations:

• close(): Closes the stream.
• flush(): Forces writing of buffered data.
• mark() and reset(): Mark a position in the stream and reset to it.
• skip(): Skips a specified number of bytes.

Example:

FileInputStream input = new FileInputStream("example.txt");
if (input.markSupported()) {
    input.mark(10); // Mark the current position
    input.skip(5);  // Skip 5 bytes
    input.reset();  // Reset to the marked position
}
input.close();

6. Java Serialization

Serialization allows objects to be converted into a stream of bytes and saved to a file. Objects must implement the Serializable interface.

Serialization Example:

class Person implements Serializable {
    private String name;
    private int age;

    Person(String name, int age) {
        this.name = name;
        this.age = age;
    }
}

// Writing an object
ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream("person.ser"));
out.writeObject(new Person("John", 30));
out.close();

Deserialization Example:

ObjectInputStream in = new ObjectInputStream(new FileInputStream("person.ser"));
Person p = (Person) in.readObject();
System.out.println("Name: " + p.name);
in.close();

7. User Interaction with the Console Class

The Console class provides a way to read user input and display output securely.

Example:

Console console = System.console();
if (console != null) {
    String userInput = console.readLine("Enter your name: ");
    char[] password = console.readPassword("Enter your password: ");
    System.out.println("Hello, " + userInput);
}

Conclusion

Java's java.io package provides robust tools to work with files, directories, and streams. By understanding and using these tools effectively, developers can handle data persistence, manipulation, and user interaction with ease.