Java - RandomAccessFile length() method

Description

The Java RandomAccessFile length() method returns the length of this file.

length() method −

• Returns the length of the file in bytes.

• Useful for checking how much data the file contains.

• Often used in file processing, truncation, or data validation tasks.

Declaration

Following is the declaration for java.io.RandomAccessFile.length() method.

public long length()

Parameters

NA

Return Value

This method returns the length of this file, measured in bytes.

Exception

IOException> − If an I/O error occurs.

Example - Usage of RandomAccessFile length() method

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

RandomAccessFileDemo.java

package com.tutorialspoint;

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

public class RandomAccessFileDemo {
   public static void main(String[] args) {
   
      try {
         // create a new RandomAccessFile with filename test
         RandomAccessFile raf = new RandomAccessFile("test.txt", "rw");

         // write something in the file
         raf.writeUTF("Hello World");

         // set the file pointer at 0 position
         raf.seek(0);

         // read and print the contents of the file
         System.out.println("" + raf.readUTF());

         // print the length of the file
         System.out.println("" + raf.length());

         // write something more in the file
         raf.writeUTF("This is an example");

         // print the length of the file
         System.out.println("" + raf.length());
      } catch (IOException ex) {
         ex.printStackTrace();
      }
   }
}

Output

Assuming we have a text file test.txt in current directory which has the following content. This file will be used as an input for our example program −

ABCDE

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

Hello World
13
33

Example - Checking file length after writing data

The following example shows the usage of RandomAccessFile length() 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("length1.txt", "rw")) {
         raf.writeUTF("Hello, World!"); // Write a UTF string

         long fileLength = raf.length(); // Get length of file
         System.out.println("Length of file in bytes: " + fileLength);
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Output

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

Length of file in bytes: 15

Explanation

• Writes a UTF string to the file.

• Calls length() to retrieve the number of bytes written.

• UTF strings contain metadata, so the length will be more than the character count.

Example - Using length() to loop through a file

The following example shows the usage of RandomAccessFile length() 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("length2.txt", "rw")) {
         raf.writeBytes("ABCDEFGH"); // 8 bytes written

         raf.seek(0); // Move pointer to start
         long len = raf.length(); // Get total length

         System.out.println("Reading file content:");
         for (int i = 0; i < len; i++) {
            char ch = (char) raf.readByte();
            System.out.print(ch + " ");
         }
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Output

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

Reading file content:
A B C D E F G H

Explanation

• Writes 8 ASCII characters to the file.

• Uses length() to determine how many bytes to read.

• Reads each byte using a loop and prints the characters.