apache/flink · error · ProgramInvocationException

The given program class does not have a main(String[]) metho

Error message

The given program class does not have a main(String[]) method.

What it means

Thrown by the PackagedProgram constructor after successfully loading the entry point class, when hasMainMethod returns false — i.e. the class has no method matching public static void main(String[]). The class resolved and loaded, but it is not a valid entry point for 'flink run'.

Source

Thrown at flink-clients/src/main/java/org/apache/flink/client/program/PackagedProgram.java:166

        this.userCodeClassLoader =
                ClientUtils.buildUserCodeClassLoader(
                        getJobJarAndDependencies(),
                        classpaths,
                        getClass().getClassLoader(),
                        configuration);

        // load the entry point class
        this.mainClass =
                loadMainClass(
                        // if no entryPointClassName name was given, we try and look one up through
                        // the manifest
                        entryPointClassName != null
                                ? entryPointClassName
                                : getEntryPointClassNameFromJar(this.jarFile),
                        userCodeClassLoader);

        if (!hasMainMethod(mainClass)) {
            throw new ProgramInvocationException(
                    "The given program class does not have a main(String[]) method.");
        }

        this.descriptor =
                new PackagedProgramDescriptor(
                        jarFile,
                        classpaths,
                        configuration,
                        savepointRestoreSettings,
                        args,
                        getMainClassName());
    }

    public PackagedProgramDescriptor getDescriptor() {
        return descriptor;
    }

    public SavepointRestoreSettings getSavepointSettings() {

View on GitHub (pinned to 2f3c205e92)

Solutions

1. Confirm the entry point class defines 'public static void main(String[] args)'.
2. If using --class, pass the fully-qualified name of the class that actually contains main(String[]).
3. If relying on the jar manifest, set 'Main-Class' (standard) or Flink's 'program-class' attribute to the correct driver class and rebuild the jar.
4. Verify the class is public top-level (or public static nested) and the method signature is exactly String[] (not String... or Object[]).

Example fix

// before
public class MyJob {
    public void run(String[] args) { ... }
}

// after
public class MyJob {
    public static void main(String[] args) throws Exception { ... }
}

private static boolean hasValidMain(Class<?> c) {
    try {
        Method m = c.getMethod("main", String[].class);
        int mod = m.getModifiers();
        return Modifier.isPublic(mod) && Modifier.isStatic(mod)
            && Modifier.isPublic(c.getModifiers());
    } catch (NoSuchMethodException e) {
        return false;
    }
}
// Call before constructing PackagedProgram:
if (!hasValidMain(MyJob.class)) {
    throw new IllegalArgumentException("MyJob lacks a public static main(String[])");
}

try {
    PackagedProgram pp = PackagedProgram.newBuilder().setJarFile(jar).build();
} catch (ProgramInvocationException pie) {
    if (pie.getMessage().contains("does not have a main")) {
        // guide user to provide --class or fix the jar manifest
    } else { throw pie; }
}

When it happens

Trigger: Constructing a PackagedProgram with an entryPointClassName (or a jar whose manifest points to a class) that lacks a conforming main(String[]) method. Also triggered when the main method exists but is not both public and static (hasMainMethod checks both).

Common situations: Pointing flink at a library JAR or an inner class instead of the real driver class. Providing a class that implements Flink interfaces (e.g. a ProcessFunction) but has no main. Manifest 'program-class'/'Main-Class' pointing to a utility class.

Related errors

• No manifest found in jar file '{jarFile.getPath()}'. The man
• Neither a '{MANIFEST_ATTRIBUTE_MAIN_CLASS}', nor a '{MANIFES
• Could not look up the main(String[]) method from the class %
• The class %s must be public.
• The class %s has no main(String[]) method.

AI-assisted analysis of apache/flink@2f3c205e92 (2026-08-14). Data as JSON: /api/errors/59deaed2c15809b4. Report an issue: GitHub.