What is Bytecode & Why Should You Learn About It? 

3 minutes

Bytecode is a low-level representation of code that’s typically generated by compilers or interpreters and processed by a virtual machine (VM) instead of a CPU or machine. Machines can’t understand bytecode, so instead, a virtual machine ​needs to ​process it and translate it into instructions for its hosting CPU.  

Bytecode is most often used in programming languages that are designed to be executed on VMs, like Java and C#. So, what else is bytecode used for and why should you understand it? Ahead, we’ll explain bytecode’s role in programming and how to get started.

Learn something new for free

Why is bytecode important? 

Flexibility and portability 

The nature of bytecode is based on the principle, “write code once, run code anywhere.” While machine code is a set of instructions for a machine, bytecode is interpreted by a VM designed for the particular hardware. As a result, the hardware can interpret universal bytecode into machine-specific instructions. 

This saves time for programmers and makes the application of bytecode more versatile and flexible than machine code. A VM can interpret bytecode to run applications on various platforms, like Windows, iOS, and Linux — so you don’t have to go through the trouble of modifying the bytecode for the target system each time. (That said, different VMs are designed for specific platforms and interpret specific bytecode formats.) 


Because bytecode runs in a virtual machine, also called a “sandbox,” it’s essentially contained in a secure environment away from hardware systems. Bytecode is generated or converted by a compiler and run by the VM, which also takes care of security. A verifier checks the code fragments for any illegal code, and run-time security checks take place when new code is loaded. ​Java, for example, has the following security features: ​ 

  • Security APIs: These contain authentication protocols and cryptographic algorithms that secure communication with the host machine. 
  • Security Manager: The manager checks the permissions and properties of each class of code and monitors the system resources. 
  • Auto Memory Management: Java automates memory management, so the programmer doesn’t have to. 
  • Compile-Time Checking: Unauthorized access results in a compile-time error rather than a crash. 
  • Cryptographic Security: Source code is verified, protected, and digitally signed, guaranteeing security. 
  • Exception Handling: Errors are reported back to the programmer, and the code will not run again until it is rectified. 
  • ClassLoader: Untrusted classes of code will not be able to behave like trusted code, adding another layer of security. 

Learn more about programming 

Bytecode is just one feature of programming that you need to know to become a software engineer. If you’re looking to make a career change or become a more efficient developer, you’ll also need the following: 

  • Basic coding. Beginners will first need a basic knowledge of coding and proficiency in at least one programming language. Since bytecode is most often run on Java, courses in Java and JavaScript might be a good place to start. 
  • Intermediate learning. You can choose to expand your knowledge of Java with an intermediate course, or you can add other languages used for bytecode, like Python
  • Advanced programming and skills. Advanced courses will help you develop your skills and enhance your portfolio. Since one of the common uses for virtual machines is running and testing new software and applications, peripheral skills in app development are also a solid choice. 

Our interactive learning is designed to facilitate the expansion of your skills and experience quickly so that you can start working as soon as possible. Check out our course catalog and get started today!

Related courses

5 courses

Related articles

4 articles

What is the Waterfall Model?

7 minutes
By Codecademy Team

T​​he waterfall model follows a linear sequential flow where each phase of development is completed and approved before the next begins. Here’s how it works.