Question

I want to use getDeclaredMethod() to find a method with this signature:

public void foo(String inArg1, Object... inArgs);

Using this call:

Class<?>[] argClasses = { String.class, Integer.class };
Method m = clazz.getDeclaredMethod("foo", argClasses);

But it generates a NoSuchMethodException exception. However, it is possible to invoke the method (assuming you find it some other way):

Object[] args = { "arg1", new Integer(2) };
m.invoke(instance, args);

I could list them all, with getDeclaredMethods(), and then try to do the signature matching myself, but that seems like a lot of work.

Should what I want to do be possible? Am I just missing something dumb?

Answer 1

The method is callable with any object(s) because it is declared to accept object(s). – But, because it is declared with Object type you won’t find via getDeclaredMethod() if you don’t search for the exact declared type.

You should be able, though, to iterate over all declared methods and check on their parameter types to see if they are assignable from your given type to find all methods which are callable with your parameters.

Example:

Class[] signature = {String.class, Integer.class};
Method[] methods = someClass.getDeclaredMethods();

for ( Method m : methods ) {
  Class[] params = m.getParameterTypes();
  if ( params.length == signature.length ) {
    int i;
    for ( i = 0; i < signature.length && params[i].isAssignableFrom( signature[i] ); i++ ) {

    }
    if ( i == signature.length ) {
      System.out.println("Found matching method: " + m.getName());
    }
  }
}

However, I have not checked which type(s) Object... actually is assignable from. I assume that it is not Integer but rather Integer[] since the varargs are compiled to arrays.