Java - RandomAccessFile read() method

Description

The Java RandomAccessFile read() method reads a byte of data from this file. The byte is returned as an integer in the range 0 to 255 (0x00−0x0ff).

read() method −

• Reads a single byte of data from the file.

• Returns −

  • The byte read, as an int (0-255)

  • -1 if end of file (EOF) is reached.

• Useful for reading raw bytes one at a time.

Declaration

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

public int read()

Parameters

NA

Return Value

This method returns the next byte of data, or -1 if the end of the file has been reached.

Exception

IOException − If an I/O error occurs. Not thrown if end-of-file has been reached.

Example - Usage of RandomAccessFile read() method

The following example shows the usage of RandomAccessFile read() 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 the first byte and print it
         System.out.println("" + raf.read());

         // set the file pointer at 4rth position
         raf.seek(4);

         // read the first byte and print it
         System.out.println("" + raf.read());
      } 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 −

0
108

Example - Read a file byte-by-byte

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_example1.txt", "rw")) {
         raf.writeBytes("ABC"); // Write some bytes

         raf.seek(0); // Move to beginning for reading
         int byteData;
         while ((byteData = raf.read()) != -1) {
            System.out.println("Read byte: " + byteData + " (char: " + (char) byteData + ")");
         }
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Output

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

Read byte: 65 (char: A)
Read byte: 66 (char: B)
Read byte: 67 (char: C)

Explanation

• Writes ABC to a file (each character = 1 byte).

• Uses read() to read each byte until EOF.

• Prints both the integer value and character.

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').