Java - RandomAccessFile class

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Introduction

The Java RandomAccessFile class file behaves like a large array of bytes stored in the file system.Instances of this class support both reading and writing to a random access file.

Class declaration

Following is the declaration for Java.io.RandomAccessFile class −

public class RandomAccessFile
   extends Object
      implements DataOutput, DataInput, Closeable

Class constructors

Class methods

Methods inherited

This class inherits methods from the following classes −

• Java.io.Object

Example - Properly closing a RandomAccessFile after writing

The following example shows the usage of RandomAccessFile close() method.

RandomAccessFileDemo.java

package com.tutorialspoint;

import java.io.RandomAccessFile;
import java.io.IOException;

public class RandomAccessFileDemo {
   public static void main(String[] args) {
      try {
         RandomAccessFile raf = new RandomAccessFile("example1.txt", "rw");

         raf.writeUTF("Hello, RandomAccessFile!");
         System.out.println("Data written to file.");

         raf.close(); // Closes the file properly
         System.out.println("File closed successfully.");
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Output

Let us compile and run the above program, this will produce the following result−

Data written to file.
File closed successfully.

Explanation

• A file named example1.txt is created (or opened), and data is written.

• close() ensures all data is flushed to disk and the file is no longer in use.

• Best practice to prevent resource leaks.

Example - Positioning the file pointer using FileChannel.position()

The following example shows the usage of RandomAccessFile getChannel() method.

RandomAccessFileDemo.java

package com.tutorialspoint;

import java.io.RandomAccessFile;
import java.nio.channels.FileChannel;
import java.io.IOException;
import java.nio.ByteBuffer;

public class RandomAccessFileDemo {
   public static void main(String[] args) {
      try (RandomAccessFile raf = new RandomAccessFile("example2.txt", "rw")) {
         raf.writeUTF("1234567890");

         FileChannel channel = raf.getChannel();
         channel.position(2); // Move to 2nd byte (inside UTF string)

         ByteBuffer buffer = ByteBuffer.allocate(8);
         int bytesRead = channel.read(buffer);  // Read 8 bytes from position 2
         buffer.flip();

         System.out.print("Data read from position 2: ");
         while (buffer.hasRemaining()) {
            System.out.print((char) buffer.get());
         }
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Output

Let us compile and run the above program, this will produce the following result−

Data read from position 2: 12345678

Explanation

• Writes data using RandomAccessFile.

• Uses the FileChannel to move the file pointer to a specific position and read from there using a ByteBuffer.

• Demonstrates how to perform non-sequential (random) file access with getChannel().

Example - Reading a specific byte using seek() and read()

The following example shows the usage of RandomAccessFile read() method.

RandomAccessFileDemo.java

package com.tutorialspoint;

import java.io.RandomAccessFile;
import java.io.IOException;

public class RandomAccessFileDemo {
   public static void main(String[] args) {
      try (RandomAccessFile raf = new RandomAccessFile("read_example2.txt", "rw")) {
         raf.writeBytes("1234567890");

         raf.seek(5); // Move file pointer to byte index 5
         int data = raf.read();
         System.out.println("Byte at position 5: " + data + " (char: " + (char) data + ")");
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Output

Let us compile and run the above program, this will produce the following result−

Byte at position 5: 54 (char: 6)

Explanation

• Writes digits 1–0 into the file.

• Seeks to byte index 5 (i.e., 6th character).

• Reads and prints the character at that position ('6').