Object is not an instance of declaring class

Question

Hi All,
I am having an issue with reflection invoking a method. I have looked up the error I am getting but cannot see why my code is throwing it. As I understand it, the error thinks I am invoking a method on the wrong instance of an expected object, but clearly my code shows I am passing the same class.
The call to field.getName() will return capitalised variables Id and Description, so that when "get" is prepended, getId and getDescription are formed. Neither method takes arguments.
I have placed a log statement gm= to find out whether the Method object has been captured, and it has. I get getId logged to the console. All fine so far until a call is made to invoke. Clearly my passed lineItemClass is causing a problem but I am not sure why, this class afterall does have getId. Have also tried changing the lineItemClass param to lineItem which is an actual instance found earlier in my code but this throws ClassCastException, even though that too has getId.
Your help appreciated!
try {
Object[] args = {};
Class[] paramTypes = {};
Class lineItemClass = lineItem.getClass();
Method getMethod = lineItemClass.
getDeclaredMethod("get" + field.getName(), paramTypes);                    
System.out.println("gm=" + getMethod.getName());
Object value = getMethod.invoke(lineItemClass, args);
} catch (Exception e) {
System.out.println("error on getFieldValue " + field.getName() + " " + e.getMessage());
}

Answer 1

You cannot overload a method with a different return type only, in this case invoke can only return an Object.
What reflection does for you is ensure that if the actual method invoked returns a primitive, that the equivalent Number type or Boolean is returned.
Number is the superclass of all primitive wrappers except Boolean, which is the wrapper for the boolean primitive type.
What reflection also does for you is ensure that although parameter values must be objects that the correct type is used in a method invocation so a method that expects an int will be invoked with a parameter of type Integer, Method.invoke ensures that the Integer value is converted to an int before the method actually is called.