Bytecode

Bytecode is an ‘intermediate representation’ of code.

Instead of directly translating high-level code (like Python or Java) into machine code that the CPU can execute, the high-level code is first compiled into bytecode.

This bytecode is fairly low-level (it mostly consists of simple instructions that a virtual machine can understand), but it’s not specific to any particular hardware architecture.

How bytecode compilers+interpreters work

When you run a program written in a language that uses bytecode (like Java or Python), the following steps usually happen:

The high-level code is compiled into bytecode by a compiler.
The bytecode is then executed by a virtual machine (VM)

So you can see that actually, bytecode languages are kind of a hybrid between compiled and interpreted languages!

Advantages of bytecode

Portability: you’ve probably heard of Java’s slogan ‘write once, run anywhere’. And even though it’s often altered to ‘write once, debug everywhere’… the original idea still stands - that Java’s bytecode can run on any platform that has a Java virtual machine (JVM) installed.
Performance: bytecode can be optimized by the virtual machine at runtime, which can lead to better performance compared to interpreted languages.
Security: it runs under a virtual machine, which might give a sandboxed environment that could prevent certainn malware attacks (or just prevent poorly written code from crashing your entire system).
Easier debugging: bytecode can retain more information about the original source code (like variable names, line numbers, etc), which can make debugging easier than debugging a fully compiled binary (anyone who’s used gdb before will understand :sigh:)

Bytecode can be used if the code needs to run on multiple platforms, so needs to be platform-independent.

Disadvantages of bytecode

It’s slower than native machine code, since it has to be interpreted or compiled at runtime by the virtual machine.
It requires a virtual machine or interpreter to run, which adds an extra layer of complexity.
All users need to install the correct virtual machine (interpreter) for the bytecode to run, which can lead to compatibility issues and general annoyance.
It can often be much less efficient in terms of RAM usage (which in this day, isn’t ideal… $600 DDR5 anyone?)
Bytecode can be reverse-engineered more easily than native machine code, so if a company wants to keep their code closed source, bytecode might not be the best choice.

Examples of bytecode languages

Java
Python
C# and other .NET languages

flashcards

Question	Answer
Question	Answer
What is bytecode?	Bytecode is an ‘intermediate representation’ of code, compiled from high-level code and executed by a virtual machine.
How do bytecode compilers and interpreters work?	1. High-level code is compiled into bytecode by a compiler. 2. The bytecode is executed by a virtual machine.
What is a key advantage of bytecode related to running on different platforms?	Portability: Bytecode can run on any platform with a compatible virtual machine (e.g., Java’s ‘write once, run anywhere’).
How does bytecode performance compare to interpreted languages?	Bytecode can be optimized by the virtual machine at runtime, leading to better performance compared to interpreted languages.
What security advantage does bytecode provide?	It runs under a virtual machine, which can provide a sandboxed environment that prevents certain malware attacks or crashes.
Why might debugging be easier with bytecode than with fully compiled binaries?	Bytecode can retain more information about the original source code, such as variable names and line numbers.
What is a key disadvantage of bytecode speed compared to native machine code?	It is slower than native machine code because it must be interpreted or compiled at runtime by the virtual machine.
What is a disadvantage related to running bytecode on a user’s system?	It requires a specific virtual machine or interpreter to be installed, which can lead to compatibility issues.
How does bytecode compare to native machine code in terms of reverse engineering?	Bytecode can be reverse-engineered more easily than native machine code.
Give three examples of languages that use bytecode.	Java, Python, C# and other .NET languages.