CODEWITHSUNDEEP
java
lak
lak

Reputation: 534

Why am I getting the "wrong number of arguments" exception when call invoke method (JAVA)

I'm trying to call a method with reflection in java, but when I call the invoke method I get an exception. This is my code:

public void start() {
    try {   
        ServerSocket server = new ServerSocket(port);

        while(true) {
            Socket s = server.accept();

            ObjectInputStream in = new ObjectInputStream(s.getInputStream());

            Class<?> myClass = Class.forName(vmi.getClass().toString().split(" ")[1]);          

            ArrayList<Object> array = new ArrayList();

            Constructor<?> cons = myClass.getConstructor(new Class<?>[] {});    


            String method = null;
            for(Method m : myClass.getMethods()) {
                method = in.readObject().toString();

                if(m.getName().equals(method)) {

                    Type return_type = m.getGenericReturnType();

                    for(Type types: m.getGenericParameterTypes()) {
                        array.add(in.readObject());
                    }
                    System.out.println(return_type);
                    if (return_type.toString().equals("void")) {                            
                         m.invoke(vmi, (Object)array);
                    }                       
                    break;
                }
            }   

        }
    } catch (IOException | ClassNotFoundException | NoSuchMethodException 
            | SecurityException | IllegalAccessException 
            | IllegalArgumentException | InvocationTargetException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();

        System.out.println("Skeleton Exception "+ e.toString());
    }
}

This is the exception:

java.lang.IllegalArgumentException: wrong number of arguments

I also tried to call the method with empty objects and the exception continues

m.invoke(vmi, new Object(), new Object());

By the way, the variables vmi and port are initialized in the constructor.

Upvotes: 1

Views: 210

Answers (1)

Erwin Bolwidt
Erwin Bolwidt

Reputation: 31299

The signature of the Method.invoke method is:

public Object invoke(Object obj, Object... args)

which is syntactic sugar for (in case you're not passing varargs) :

public Object invoke(Object obj, Object[] args)

You are, however, passing (Object,Object) -> this will take the second object as a single argument for a varargs, so your call is translated by the compiler into m.invoke(vmi, new Object[] { array }).

Complicating your code is the fact that you have a variable called array, but its type is actually ArrayList, which is not an array.

You can change your code to:

m.invoke(vmi, array.toArray());

This will pass your arguments as the whole varargs argument args rather than as an individual element in the varargs array.

Upvotes: 1

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