jruby/jruby · error · ArgumentError

argument count mismatch for method signature {}

Error message

argument count mismatch for method signature {}

What it means

Error "argument count mismatch for method signature {}" thrown in jruby/jruby.

Source

Thrown at core/src/main/java/org/jruby/java/proxies/JavaProxy.java:433

        final int argsLen = argc - 2;

        checkArgSizeMismatch(runtime, argsLen, argTypesAry);

        Class[] argTypesClasses = (Class[]) argTypesAry.toArray(new Class[argsLen]);

        Object[] javaArgs = new Object[argsLen];
        for ( int i = 0; i < argsLen; i++ ) {
            javaArgs[i] = args[i + 2].toJava( argTypesClasses[i] );
        }

        JavaMethod method = new JavaMethod(runtime, getMethod(context, name, argTypesClasses));
        return method.invokeDirect(context, getObject(), javaArgs);
    }

    private static void checkArgSizeMismatch(final Ruby runtime, final int expected, final RubyArray argTypes) {
        if ( argTypes.size() != expected ) {
            Class[] argTypesClasses = (Class[]) argTypes.toArray(new Class[argTypes.size()]);
            throw JavaMethod.newArgSizeMismatchError(runtime, argTypesClasses);
        }
    }

    @JRubyMethod
    public IRubyObject java_method(ThreadContext context, IRubyObject rubyName) {
        String name = rubyName.asJavaString();

        return getRubyMethod(context, name);
    }

    @JRubyMethod
    public IRubyObject java_method(ThreadContext context, IRubyObject rubyName, IRubyObject argTypes) {
        String name = rubyName.asJavaString();
        RubyArray argTypesAry = argTypes.convertToArray();
        Class[] argTypesClasses = (Class[]) argTypesAry.toArray(new Class[argTypesAry.size()]);

        return getRubyMethod(context, name, argTypesClasses);
    }

View on GitHub (pinned to fb650c13e0)

Solutions

1. The argument count does not match the Java method signature. Supply exactly the number of parameters the target method declares.

When it happens

Trigger: Thrown at core/src/main/java/org/jruby/java/proxies/JavaProxy.java:433 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of jruby/jruby@fb650c13e0 (2026-08-23). Data as JSON: /api/errors/dde8bf1caeb1daaf. Report an issue: GitHub.