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What is a Bytecode?

Bytecode is a form of instruction set designed for efficient execution by a software interpreter or a virtual machine. Unlike machine code, which is directly executed by the CPU, bytecode is typically portable and platform-independent, making it a cornerstone of modern programming languages like Java. Intrigued? Discover how bytecode powers the flexibility and versatility of your favorite applications.
Troy Holmes
Troy Holmes

Bytecode is software computer object code that can only be interpreted by a software program, typically described as virtual machine. In many modern software development platforms, bytecode is preferred to low-level machine code as it places an interpreter between the software program and the computer hardware. Machine code is platform-dependent which requires compilation on each hardware platform to execute properly on that specific platform.

As the software development paradigms have matured over time, so too has the use of external layers of interpretation between the hardware of a computer and the software that runs on the computer. At the beginning of early software creation, developers were dependent on computer hardware, drivers and the underlying operating systems. This dependency forced the developers to intimately understand many aspects of the specific computers, which made platform independence very difficult and software growth tightly coupled to specific vendors of hardware and software.

Man holding computer
Man holding computer

The creation of bytecode has created an environment of platform independence in the software development community. With the use of this metaphor, software developers can write once and use everywhere. Developers are not forced to understand the native drivers of a specific computer, nor are they concerned with the underlying operating system on which the software will run.

A virtual machine is the term used in the Java™ programming language to represent the software program that will interpret the bytecode. This virtual machine will convert the bytecode as necessary to interact with the underlying hardware and operating system within the computer. The machine code that is generated by the virtual machine is hidden from the developer of the Java™ software program and can fully function on multiple platforms without requiring a rewrite of the software application for each platform.

The internals of bytecode are more of an advance topic and not typically necessary from most developers to understand. Bytecode is not a human readable language and consists of numeric encoded representations of classes, methods and the scope of the objects and their nesting within classes. Each bytecode opcode is one single byte in length.

The machine language required for modern computers to function on commands is proprietary in nature by vendor. Each hardware and operating system has a unique way of handling processes, memory allocation, and task utilization. By using a bytecode software development application, the virtual machine interpreter is responsible for creating the machine code that will be required to run on the proprietary platform.

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Discussion Comments


@everetra - I will say this about the issue of software speed of execution. While I hate to admit it, it’s becoming less and less important.

That’s because computers are becoming faster and faster. Unfortunately this makes for some lazy programming practices. Programmers don’t focus as much on optimizing their code. That’s the downside.

It used to be (back in my days) that you would tweak every bit of memory performance out of your code. Now it’s all about bells and whistles in my opinion.


@Mammmood - I’ve never messed with Java. But I have done some fiddling with .NET. Compiling programs in a .NET environment is similar to Java in many respects, but .NET is also a bytecode environment.

You can use different programming languages like C# or VB.NET and then they will compile down to the .NET runtime environment. It’s a layer between the computer and the end user, just like Java.

There is one big difference however. At least at this moment, you can’t run .NET programs everywhere. I think there is a port for Linux, but that hasn’t been widely deployed yet, I don’t think. I believe that it’s a work in progress. So Java still wins hands down in my opinion when it comes to bytecode manipulation.

@SkyWhisperer - You are correct. Bytecodes are not used because they provide for speed. They are used because they provide for flexibility.

A Java virtual machine can run in any environment: Mac, Linux, and Windows. This means that if you create a Java program then that program can run in any environment even if you don't have that particular operating system.

That means that you have a bigger market within which to sell your software. That’s why you see that a lot of Java programs run in your Internet browser. The program doesn’t care what computer your browser is installed on, as long as Java is on your system.

Does it make for fast programs? I don’t think so, but that’s not the name of the game here.


I’ve been asked to learn Java and have heard a little bit about this whole Java Virtual machine and the JVM bytecode environment. I guess I understand the basic concept but don’t really understand why we need it.

By creating bytecodes you are creating an extra layer between the computer and the user, right? In that case, you’re creating programs that will invariably run slower. I was told that Java programs are notoriously slow.

I don’t get why it’s so necessary to have a virtual machine environment. Supposedly computer programs are supposed to run faster, not slower, isn’t that right?

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