Reflections: Method.invoke + complex and primitive args

[Michael Herrmann]

Method.invoke(Object obj, Object[] args) allows to dynamically invoke a method on an object. But what if the method to be invoked looks like, for instance

public void myMethod(Object arg1, int i) {}

? Is it really true that, because int is not a subclass of Object, you cannot dynamically call methods that use complex as well as primitive datatypes for their parameters?

Thanks in advance.
[ September 12, 2004: Message edited by: Michael Herrmann ]

[Sheldon Fernandes]

? Is it really true that, because int is not a subclass of Object, you cannot dynamically call methods that use complex as well as primitive datatypes for their parameters?

No, not at all. If a method has a primitive as an argument, you pass the wrapped version to method.invoke().

So, for the method:

public void myMethod(Object arg1, int i) {}

the call would look something like this.

method.invoke(obj, new Object[] {arg1, new Integer(i)})

See the documentation for method.invoke()
[ September 12, 2004: Message edited by: Sheldon Fernandes ]

[Michael Herrmann]

I should have read the docu more carefully. Thank you.

Is there a similar option for Class.getMethod?(I mean this complex-primitive conversion). What I want to do is to add an assertThrows functionality to JUnit's Assert class. My current, not working approach looks like this:

static public void assertThrows(String message, Object o, String methodName, Object[] args, Class c) {
        boolean exceptionThrown = false;
        try {
            Class[] argsClasses = new Class[args.length];
            for(int i=0;i<args.length;i++) {
                argsClasses[i] = args[i].getClass();
            }
            Method m = o.getClass().getMethod(methodName, argsClasses);
            m.invoke(o, args);
        } catch(InvocationTargetException e) {
            if(c.isInstance(e.getCause()))
                exceptionThrown = true;
        } catch(IllegalAccessException e2) {
        } catch(NoSuchMethodException e3) {
        }
        assertTrue(message, exceptionThrown);
    }

Because the primitives are also represented as Class objects, Class.getMethod seems not to provide the conversion(complex->primitive) functionality. The problem is that the args above are passed in as Objects, which can be handled(=converted) by Method.invoke, but not by Class.getMethod.

[Sheldon Fernandes]

For objects you can call the getClass() method to get the runtime class of an object. For primitives you can use the literal xxx.class

Class[] argClasses = new Class[] {obj.getClass(), int.class, Integer.class}

You will probably need to change the signature to accept Class[]. If you try to obtain it from Object[], you will not know which wrappers were actually primitives.

I hope that makes sense.

[Edit] More on the class Class
[ September 12, 2004: Message edited by: Sheldon Fernandes ]