JAVA: Calling Unknown Object Class Method and Passing it's Parameters

Question

The objective is simple, I want to create a method which load a class dynamically, access its method and passing their parameters value and getting the return value at run-time.

Class which will be called

class MyClass {

    public String sayHello() {

        return "Hello";
    }

    public String sayGoodbye() {

        return "Goodbye";
    }

    public String saySomething(String word){
        return word;
    }
}

Main Class

public class Main {


    public void loadClass() {
        try {

            Class myclass = Class.forName(getClassName());

            //Use reflection to list methods and invoke them
            Method[] methods = myclass.getMethods();
            Object object = myclass.newInstance();

            for (int i = 0; i < methods.length; i++) {
                if (methods[i].getName().startsWith("saySome")) {
                    String word = "hello world";

                    //**TODO CALL OBJECT METHOD AND PASS ITS PARAMETER**
                } else if (methods[i].getName().startsWith("say")) {

                    //call method
                    System.out.println(methods[i].invoke(object));
                }

            }

        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }

    private String getClassName() {

        //Do appropriate stuff here to find out the classname

        return "com.main.MyClass";
    }

    public static void main(String[] args) throws Exception {

        new Main().loadClass();
    }
}

My question is how to invoke method with parameters and passing its value? also getting the return value and its type.

viralpatel.net/blogs/…

Markus Lausberg
– Markus Lausberg

2012-12-10 07:19:00 +00:00
Commented Dec 10, 2012 at 7:19 — Markus Lausberg
– Markus Lausberg, Commented Dec 10, 2012 at 7:19
System.out.println(methods[i].invoke(object, word));

assylias
– assylias

2012-12-10 07:23:08 +00:00
Commented Dec 10, 2012 at 7:23 — assylias
– assylias, Commented Dec 10, 2012 at 7:23

Jon Skeet · Accepted Answer · 2012-12-10 07:20:16Z

4

I think you're just missing the fact that you can pass in arguments to invoke, as an Object[]:

Object result = methods[i].invoke(object, new Object[] { word });

Or using varargs, if you prefer:

Object result = methods[i].invoke(object, word);

(The above two calls are equivalent.)

See the documentation for Method.invoke for more details.

answered Dec 10, 2012 at 7:20

Jon Skeet

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1 Comment

Angga Saputra Over a year ago

that's it, yes my mistake.. the second param of methods[i].invoke is for the arguments..thanks Jon

Murali N · Accepted Answer · 2012-12-10 07:18:31Z

1

simply create the object of MyClass invoke the function like this

MyClass mc = new MyClass();
String word = "hello world";
String returnValue = mc.saySomething(word);
System.out.println(returnValue);//return hello world here

or do this

Class myclass = Class.forName(getClassName());
Method mth = myclass.getDeclaredMethod(methodName, params);
Object obj = myclass.newInstance();
String result = (String)mth.invoke(obj, args);

answered Dec 10, 2012 at 7:18

Murali N

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Comments

Sashi Kant · Accepted Answer · 2012-12-10 07:19:46Z

0

Try ::

Class c = Class.forName(className); 
Method m = c.getDeclaredMethod(methodName, params);
Object i = c.newInstance();
String result = (String)m.invoke(i, args);

answered Dec 10, 2012 at 7:19

Sashi Kant

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