Java reflection when a method has a variable arglist

Question

I've got something along the lines of the following:

public class A { 
    public void theMethod(Object arg1) {
        // do some stuff with a single argument
    }
}

public class B {
    public void reflectingMethod(Object arg) {
        Method method = A.class.getMethod("theMethod", Object.class);
        method.invoke(new A(), arg);
    }
}

How do I modify that so that I can do the following instead?

public class A { 
    public void theMethod(Object... args) {
        // do some stuff with a list of arguments
    }
}

public class B {
    public void reflectingMethod(Object... args) {
        Method method = A.class.getMethod("theMethod", /* what goes here ? */);
        method.invoke(new A(), args);
    }
}

That worked. I'd tried it before but gotten stumped at how to get the class for List<Object>, since ".class" isn't allowed on generics. Creating a new empty arraylist works though (as long as the method signatures use ArrayList<Object> for the arguments. — Ginger McMurray
– Ginger McMurray, Commented Dec 6, 2011 at 19:18
@Darthenius, well a List is not really a varargs :-) btw, James, you should be able to look up the method (with List) by doing List.class I guess... — aishwarya
– aishwarya, Commented Dec 6, 2011 at 20:06

Ransom Briggs · Accepted Answer · 2011-12-06 18:46:55Z

5

A.class.getMethod("theMethod", Object[].class);

answered Dec 6, 2011 at 18:46

Ransom Briggs

3,1053 gold badges36 silver badges46 bronze badges

Sign up to request clarification or add additional context in comments.

6 Comments

Andy Thomas Over a year ago

It's the callee you're looking for ... not a particular caller.

Ransom Briggs Over a year ago

With reflection, the method that is returned is the one with a matching method name and parameters. In this case, the method name is theMethod and the parameters is an object array. If you pass invoke different subclasses classes of Object it will not care.

Ginger McMurray Over a year ago

Object[].class caused an exception when trying to invoke the reflected method if I passed in more than one item in the array. For instance a String[] of {"a", "b", "c"} complained that there were too many arguments (it expected 1 but got three).

Ginger McMurray Over a year ago

I'll move this to an answer once the system will let m: Darthenius's suggestion in the comments for the original question worked, once I wrapped my head around how to do it. public class A { public void theMethod(ArrayList<Object> args) { // do stuff } } public class B { public void reflectingMethod(ArrayList<Object> args) { Method method; try { method = A.class.getMethod("theMethod", args.getClass()); method.invoke(new A(), args); } catch (Exception e) { } } }

aishwarya Over a year ago

@JamesMcMurray, you can actually use varargs. Just invoke the method wrapping the args inside a Object[] e.g. method.invoke(new A(), new Object[] {new Object[] { "a", "b", "c" }} ). Basically, invoke method also takes varargs so can confuse where the array is directed.

|

Ginger McMurray · Accepted Answer · 2011-12-07 21:03:03Z

0

Darthenius's suggestion in the comments for the original question worked, once I wrapped my head around how to do it.

public class A {
    public void theMethod(ArrayList<Object> args) { // do stuff 
    }
}

public class B {
    public void reflectingMethod(ArrayList<Object> args) {
        Method method;
        try {
            method = A.class.getMethod("theMethod", args.getClass());
            method.invoke(new A(), args);
        } catch (Exception e) {}
    }
}

answered Dec 7, 2011 at 21:03

Ginger McMurray

1,1672 gold badges20 silver badges43 bronze badges

Collectives™ on Stack Overflow

Java reflection when a method has a variable arglist

2 Answers 2

6 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

6 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related