Java coding trouble!

I'm having trouble writing some helper methods. so I have an arraylist and have been asked to write a few methods that I've described below.

ArrayList measurements = new ArrayList();

1. A public method called countAbove(). This method takes one argument, a double value called threshold. This method returns an int value for the number of elements in measurements that exceed the value of threshold. It performs this by calling a private helper method (which you also need to define) that uses head recursion to traverse the values of the measurements attribute. 2. A public method called countBelow(). This method takes one argument, a double value called threshold. This method returns an int value for the number of elements in measurements that are less than the value of threshold. It performs this by calling a private helper method (which you also need to define) that uses tail recursion to traverse the values of the measurements attribute.

I am having issues with my recursion. Any help is appreciated.