WebAssembly and Java: Why Learn Java if WebAssembly Exists?

WebAssembly and Java: What It Is and Why You Should Know About It

When we talk about web development, the trio that usually comes to mind is HTML, CSS, and JavaScript. But the world doesn't stand still. Technologies are emerging that turn conventional ideas about what can run in a browser upside down. One of these is WebAssembly (or simply WASM). And if you are studying Java, it is doubly interesting to learn how these two technologies intersect.

In this article, we won't dive into the intricacies of compilers and bytecode. We will talk about what WebAssembly is, why it is needed, and how Java can (or cannot) be friends with it. You will learn why experienced developers are increasingly looking towards WASM, and you will see code examples in Java that will help you understand the difference.

What is WebAssembly in Simple Terms

Imagine that a browser is a small computer. Previously, only one program could run on this computer — JavaScript. It is slow, but flexible. WebAssembly is a new "processor" for this computer. It allows you to run code written in C, C++, Rust, or even Java, at near-native speed. That is, almost like a regular program on your PC, but inside a browser.

WASM is not a programming language. It is a binary instruction format. You write code in a familiar language (e.g., Java), compile it into WASM, and the browser executes these instructions at a speed unattainable for JavaScript.

Why is WebAssembly Needed if Java Exists?

Excellent question. After all, Java has its own virtual machine (JVM), which also compiles bytecode and does it quickly. Why do we need another "virtual machine"?

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• Browser environment: The JVM does not work directly in the browser (without plugins, which are no longer supported). WebAssembly does. If you want to run heavy computations on the frontend (e.g., video processing, 3D rendering, or encryption), WASM is your choice.
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• Performance: WebAssembly loads and executes faster than JavaScript, and can be faster than Java applets of the past. It is closer to the "metal".
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• Versatility: You are not tied to one language. Wrote in C++ — compiled to WASM. Wrote in Rust — same. Theoretically, Java can be too, although it is more difficult.
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WebAssembly and Java: Is There a Direct Connection?

There is a nuance here. There is no direct compilation of Java to WebAssembly "out of the box". The JVM is a huge and complex system. To run Java in a browser via WASM, you either need to compile the JVM itself into WASM (which projects like CheerpJ do), or rewrite the code in another language. But this does not mean that Java and WASM do not intersect.

In fact, understanding WebAssembly gives a Java developer a huge advantage. You begin to see the boundaries of the JVM's capabilities and understand where it is worth using other tools.

Example 1: Speed Comparison (Conceptual Java Code)

Imagine you need to calculate the factorial of a large number. In Java, it looks like this:

public class FactorialExample {\n    public static long factorial(int n) {\n        if (n <= 1) return 1;\n        return n * factorial(n - 1);\n    }\n\n    public static void main(String[] args) {\n        long start = System.nanoTime();\n        long result = factorial(20);\n        long end = System.nanoTime();\n        System.out.println("Java Result: " + result);\n        System.out.println("Time: " + (end - start) + " ns");\n    }\n}\n

This code runs on the JVM. It is fast, but the JVM needs time to start up and warm up. There is no such code in the browser. If we wanted to do the same on the frontend, we would have to write it in JavaScript. And with We