Java.Streams.What do you know about RandomAccessFile?

📘 What is RandomAccessFile?

• It’s part of java.io.
• Supports both reading and writing.
• Allows you to move the file pointer to read/write anywhere (random access).
• Acts like a combination of DataInputStream + DataOutputStream + file pointer control.

🔧 Constructor

RandomAccessFile(File file, String mode)
RandomAccessFile(String name, String mode)

📜 Modes:

• "r" → read-only
• "rw" → read + write
• "rws" → read/write with synchronous updates to file & metadata
• "rwd" → read/write with synchronous updates to file data only

🔑 Key Features & Methods

Method	Description
readXxx()	Read primitives: readInt(), readDouble(), readUTF()
writeXxx()	Write primitives: writeInt(), writeBoolean(), writeUTF()
seek(long pos)	Move the file pointer to position pos
getFilePointer()	Returns current file pointer position
length()	Returns the total file length in bytes
setLength(long newLength)	Truncates or extends the file

✅ Example: Read and Write with RandomAccessFile

import java.io.RandomAccessFile;

public class RandomAccessDemo {
    public static void main(String[] args) throws Exception {
        RandomAccessFile raf = new RandomAccessFile("data.bin", "rw");

        // Write data
        raf.writeInt(42);
        raf.writeUTF("Hello, Stanley!");

        // Move to the beginning
        raf.seek(0);

        // Read data
        int number = raf.readInt();
        String message = raf.readUTF();

        System.out.println("Number: " + number);
        System.out.println("Message: " + message);

        raf.close();
    }
}

📦 Use Cases

Use Case	Why RandomAccessFile
Large file manipulation	Read/write without loading whole file
Fixed-size record storage	Access specific record by position
Database/index structures	Jump to index offsets directly
Append at specific offset	Seek to the end or anywhere

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⚠️ Caveats

• Not buffered (low-level)
• Not thread-safe unless synchronized externally
• Should be closed manually (no AutoCloseable until Java 7)

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🧵 TL;DR

Feature	RandomAccessFile
Supports read/write?	✅ Yes
Move to specific position?	✅ Yes (seek())
Good for?	File editing, logs, databases
Stream-based?	❌ No (it’s a direct file API)
Char encoding?	❌ Manual (not charset-aware like Reader)