Java - RandomAccessFile readByte() method

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Description

The Java RandomAccessFile readByte() method reads a signed eight-bit value from this file. This method reads a byte from the file, starting from the current file pointer.

Declaration

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

public final byte readByte()

Parameters

NA

Return Value

This method returns the next byte of this file as a signed eight-bit byte.

Exception

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

• EOFException − If this file has reached the end.

Example - Usage of RandomAccessFile readByte() method

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

RandomAccessFileDemo.java

package com.tutorialspoint;

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

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 byte
         System.out.println(raf.readByte());

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

         // write 0 at the start
         raf.write(0);

         // read byte
         System.out.println(raf.readByte());
      } 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
11

Example - Reading bytes from a file one by one

The following example shows the usage of RandomAccessFile readByte() 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("sample.dat", "rw");

         // Write some bytes for demonstration
         raf.writeByte(65); // 'A'
         raf.writeByte(66); // 'B'
         raf.writeByte(67); // 'C'

         // Reset file pointer to the start
         raf.seek(0);

         // Read and print each byte
         System.out.println("Byte 1: " + (char) raf.readByte()); // A
         System.out.println("Byte 2: " + (char) raf.readByte()); // B
         System.out.println("Byte 3: " + (char) raf.readByte()); // C

         raf.close();
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Output

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

Byte 1: A
Byte 2: B
Byte 3: C

Explanation

• writeByte() writes raw bytes into the file.

• readByte() reads one byte at a time and returns it as a signed byte (-128 to 127).

• We cast it to char for readable output (prints A, B, C).

• This is useful when dealing with low-level binary file formats.

Example - Reading a signed byte and checking its value

The following example shows the usage of RandomAccessFile readByte() 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("numbers.dat", "rw");

         // Write byte values (some negative)
         raf.writeByte(127);   // Max positive byte
         raf.writeByte(-128);  // Min negative byte
         raf.writeByte(-1);    // -1 in byte is 0xFF

         // Reset pointer
         raf.seek(0);

         byte b1 = raf.readByte();
         byte b2 = raf.readByte();
         byte b3 = raf.readByte();

         System.out.println("First byte: " + b1);  // 127
         System.out.println("Second byte: " + b2); // -128
         System.out.println("Third byte: " + b3);  // -1

         raf.close();
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Output

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

First byte: 127
Second byte: -128
Third byte: -1

Explanation

• readByte() returns a signed byte, which can be negative.

• This example shows how byte values over 127 (like 0xFF, 0x80) are interpreted as negative numbers.

• Useful in networking, bytecode, or any protocol that uses signed byte data.