java: get class which instantiates current class using reflection

I'm trying to create a method(B) in one class(B) which, when invoked in a different class(A) : will ask a user for input and then invoke a method(A) in the class(A) which invoked it.

Kind of like this:

A:

public class ExampleClass {
    public final int ACTIVITIES = 2;  
    public static void main(String[] args) {
        Selector instance = new Selector();
        instance.getActivity(ACTIVITIES);
    }
    public void Activity1(int input) {
    // does stuff (Not pertinent)
    }
    public void Activity2(int input) {
    // does other stuff (Not pertinent)
    }
}

B:

public class Selector {
    public void getActivity(int activities) {
        int[] input = Selector.getInput(activities);
        // run the appropriate method based on input[0] with the parameter input[1]
    }
    private static int[] getInput(int activities) {
        // sets input[0] from user for Activity method (Not pertinent)
        // sets input[1] from user for the Activity method's param (Not pertinent)
        return input[];
    }
}

The name of the method to be invoked is: "Activity"+Input[0] hence the method names in ExampleClass (ACTIVITIES is used to limit the input to existing methods).

Recap: when ExampleClass instantiates getActivity : getActivity needs to invoke either Activity1 or Activity2 with an int parameter based on the user's input.