Your First Program

This walkthrough takes you from a .java source file to running output on CratonVM.

1. Write a Java program

// HelloWorld.java
public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello from CratonVM!");
        for (String arg : args) {
            System.out.println("arg: " + arg);
        }
    }
}

2. Compile it

CratonVM runs bytecode, so you compile with a standard Java compiler (javac from any JDK 8+):

javac HelloWorld.java

This produces HelloWorld.class.

3. Run it on CratonVM

cratonvm --classpath . HelloWorld

Hello from CratonVM!

Pass program arguments after the class name:

cratonvm --classpath . HelloWorld one two three

Hello from CratonVM!
arg: one
arg: two
arg: three

Note: class names use dots, not slashes or file paths: com.example.Main, not com/example/Main or com/example/Main.class.

Running from the source tree

If you built from source and have not installed the binary, you can run it directly through Cargo:

cargo run --release -p cratonvm-cli -- --classpath . HelloWorld

Everything after -- is passed to CratonVM verbatim. Always use --release for anything performance-sensitive — debug builds are 10–50× slower.

Running a JAR

If your program is packaged as a JAR with a Main-Class in its manifest, run it with --jar. The classpath flag is ignored in this mode (the main class comes from ../../../../apps/META-INF/MANIFEST.MF):

cratonvm --jar app.jar arg1 arg2

Common next options

See the Command-Line Reference for the full list, and Running Programs for classpaths, JARs, modules, and argument files in depth.