Java Writing Bytes to a File

Being able to write bytes to a file is useful if you need to create a non-text file. As always with Java, there are many of doing this. The following is one of the simplest ways to create a file and write some bytes to it.

Writing a Byte Array to a File

In general, it is unlikely you will write individual bytes to a file. The full example below writes the contents of a byte array to file. These are the two key lines:

// This is our byte array, so we can view the output, these are ASCII codes for the letters A B C
byte letters[]={65,66,67};

// This writes the entire array to the file (stream) opened
fo.write(letters);

To make it easier to demonstrate, the output file created by our full program can be opened in a text editor. The array of bytes could just have easily been a file header, pixels of a bitmap or any other kind of binary blob.

Full Java Program

With the Java JDK installed, from a command line:

• Save the following as writebytes.java
• Compile with javac writebytes.java
• Run with java Writebytes

If you do not have Java JDK installed, click the following link to find out how to install Java on your computer!

import java.io.*;

class Writebytes{
	public static void main(){
		final String myfile="output2.txt";
		
		// This following are ASCII codes for the letters A B C
		byte letters[]={65,66,67};
		
		try(var fo = new FileOutputStream(myfile)){
			fo.write(letters);
			System.out.println("File "+myfile+" saved!");			
		}catch(IOException e){
			// Problem writing file...
			System.out.println("There was a saving "+myfile);
			System.out.println(e);
		}
	}
}

Updated (30/10/2026)

Java File Handling:
Read Text | Write Text | Read Binary | Write Binary