How to invoke method with variable arguments in java using reflection?

Question

I'm trying to invoke a method with variable arguments using java reflection. Here's the class which hosts the method:

public class TestClass {

public void setParam(N ... n){
    System.out.println("Calling set param...");
}

Here's the invoking code :

try {
        Class<?> c = Class.forName("com.test.reflection.TestClass");
        Method  method = c.getMethod ("setParam", com.test.reflection.N[].class);
        method.invoke(c, new com.test.reflection.N[]{});

I'm getting IllegalArgumentException in the form of "wrong number of arguments" at the last line where I'm calling invoke. Not sure what I'm doing wrong.

Any pointers will be appreciated.

• Thanks

Answer 1

public class Test {

public void setParam(N... n) {
    System.out.println("Calling set param...");
}

/**
 * @param args the command line arguments
 */
public static void main(String[] args) throws Exception {
    Test t=new Test();
    Class<?> c = Class.forName("test.Test");
    Method  method = c.getMethod ("setParam", N[].class);
    method.invoke(t, (Object) new N[]{});
}
}

Works for me.

1. Cast your N[] to Object
2. call invoke on instance, not on class

Answer 2

There is no TestClass instance in your code snippet on which the methd is invoked. You need an instance of the TestClass , and not just the TestClass itself. Call newInstance() on c , and use the result of this call as the first argument of method.invoke() .

Moreover, to make sure your array is considered as one argument, and not a varargs, you need to cast it to Object:

m.invoke(testClassInstance, (Object) new com.test.reflection.N[]{});