Java Academy · Lesson

Building a Native Image

Ahead-of-time compilation.

Building a Native Image is a free Java Academy lesson on CoddyKit — lesson 2 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Java Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Building a Native Image

The native-image tool turns compiled Java bytecode into a single, self-contained native executable. This lesson walks through the build process, what happens under the hood, and how to run the result.

Start with Ordinary Java

Native image begins from normal compiled classes. Here is a plain program we will imagine compiling to native code.

public class Hello {
    public static void main(String[] args) {
        System.out.println("Hello from a native binary!");
    }
}

Compile, Then Build

The two steps: first javac Hello.java produces Hello.class; then native-image Hello produces an executable named hello. The build is much slower than compilation because it analyzes the whole program.

Closed-World Analysis

native-image performs closed-world analysis: it must see all code that could ever run. Starting from main, it walks every reachable method and includes only those in the binary. Anything unreachable is removed (dead-code elimination at link time).

Ahead-of-Time Compilation

Reachable methods are compiled to native machine code ahead of time. Because there is no bytecode left to interpret and no JIT, there is also no warmup — the program runs at full speed from its first instruction.

Build-Time Initialization

To start fast, native-image can run static initializers at build time and bake the resulting heap into the image (the image heap). This means some objects already exist the instant the program launches.

Running the Executable

The output is an ordinary OS executable. You run it directly — no java -jar, no JVM install required on the target machine. It is also fully static or mostly static depending on flags.

Common Build Flags

Useful options include:

-o name — output file name.
--no-fallback — fail rather than emit a JVM-dependent fallback image.
-O2 / -O3 — optimization level.
--static — fully statically linked binary (Linux).

Memory and Disk

The build itself is memory-hungry — large applications can need several gigabytes of RAM and minutes of CPU. This cost is paid once at build time, in exchange for cheap, fast runtime startup.

Building via Maven/Gradle

In real projects you rarely call native-image by hand. The GraalVM native-build-tools plugins integrate it into Maven (native:compile) and Gradle (nativeCompile) so the binary is part of your normal build pipeline.

Verifying Startup

After building, compare startup: a java -jar launch may take hundreds of milliseconds while the native binary returns in single-digit milliseconds. Measuring this difference is the whole point of going native.

Quick Check

Test your understanding of building native images.

Recap

You learned the native-image build:

Start from compiled bytecode; native-image produces a self-contained executable.
Closed-world analysis finds all reachable code from main.
Reachable code is AOT-compiled; unreachable code is removed.
Build-time initialization bakes an image heap for fast startup.
The build is slow and memory-hungry; integrate it via Maven/Gradle plugins.

Frequently asked questions

Is the “Building a Native Image” lesson free?

Yes — the full text of “Building a Native Image” is free to read here on the web, and the Java Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Java Academy course, upgrade to CoddyKit PRO.

What will I learn in “Building a Native Image”?

Ahead-of-time compilation. You practise Java Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Java Academy?

No prior experience is required. Java Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 2 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Building a Native Image” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Java Academy lesson?

Yes. Every Java Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

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