JavaBean setter method invocation error "wrong number of arguments"

Question

Im trying to set indexed value of JavaBean and i cannot do that with reflection. Any ideas why is this happening? How to invoke setter by reflection?

public class Bean1111 {
    public void setColors(Color[] colors) {
        this.colors = colors;
    }
    public Color [] colors = {Color.RED, Color.green, Color.blue, Color.pink};

    public static void main(String[] args) throws InvocationTargetException, IllegalAccessException {
        Bean1111 bean = new Bean1111();
        Color[] colors = new Color[]{Color.RED,Color.BLACK};
        bean.getClass().getDeclaredMethods()[0].invoke(bean, colors); //exception  "java.lang.IllegalArgumentException: wrong number of arguments"
    }
}

for some reason if i'll do this code, compiler just inline my array as an multiple objects, but not as an array object

// with the same bean class
 public static void main(String[] args) throws Exception {
        Bean1111 bean = new Bean1111();
        Color[] colors = new Color[]{Color.RED,Color.BLACK, Color.WHITE};
        Expression expr = new Expression(bean, "setColors", colors);
        expr.execute();
        // java.lang.NoSuchMethodException: <unbound>=Bean1111.setColors(Color, Color, Color);
    }

Try checking `bean.getClass().getDeclaredMethods()[0].getName()`. — Andrew S, May 14 '19 at 16:22
First, make sure you actually call the setter, and not main(). Second, change the type of colors to Object (or cast it to Object), to make sure the array is not interpreted as an array of two arguments, but as a single argument. — JB Nizet, May 14 '19 at 16:25
try `bean.getClass().getDeclaredMethods()[0].invoke(bean, new Object[] {colors});` — Michał Krzywański, May 14 '19 at 16:25

Michał Krzywański · Accepted Answer · 2019-05-15T08:47:47.837

You should use

bean.getClass().getDeclaredMethods()[0].invoke(bean, new Object[] {colors});

Or :

bean.getClass().getDeclaredMethods()[0].invoke(bean, (Object) colors);

As invoke method takes varargs parameter you to have explicitly tell that your array is a single argument for invoked method.

When adding a getter method to your Bean1111 class and then printing the result :

Arrays.stream(bean.getColors()).forEach(System.out::println);

It gives the output :

RED
BLACK

JavaBean setter method invocation error "wrong number of arguments"

1 Answers1