JUnit exception "Object is not an instance of declaring method"

Question

I have the next JUnit test, but when I execute it throws "Object is not an instance of declaring method". What could it be?

@Test
    public void testCopiarByteArray() throws IllegalAccessException, IllegalArgumentException, InvocationTargetException, NoSuchMethodException, SecurityException, InstantiationException, UnsupportedEncodingException{
        String expected = "prueba";
        String mensaje = "prueba";

        DataReader datareader = new DataReader(null, null, 100, "=");

        Method copiarByteArray = datareader.getClass().getDeclaredMethod("copiarByteArray", byte[].class, int.class);
        copiarByteArray.setAccessible(true);

        byte[] copia = (byte[]) copiarByteArray.invoke(mensaje.getBytes(), mensaje.getBytes().length);

        String actual = new String(copia, "UTF-8");

        assertEquals("failure - encription not correctly encript", expected, actual);
    }

janos · Accepted Answer · 2016-05-29 17:44:57Z

1

The first parameter of .invoke should be an instance of the object to invoke the method on.

So instead of:

    byte[] copia = (byte[]) copiarByteArray.invoke(mensaje.getBytes(), mensaje.getBytes().length);

You need to add datareader as first parameter:

    byte[] copia = (byte[]) copiarByteArray.invoke(datareader, mensaje.getBytes(), mensaje.getBytes().length);

answered May 29, 2016 at 17:44

janos

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GhostCat · Accepted Answer · 2016-05-29 17:44:40Z

0

Check the javadoc on reflection APIs.

You have to pass the object to call your method on as first parameter; and then followed by the "actual" method parameters.

Your code tries to execute a method on mensaje.getBytes(); which of course will not work.

answered May 29, 2016 at 17:44

GhostCat

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