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').