import java.util.List;
import java.util.ArrayList;
 
class Ideone
{
	public static float myAverage(List<Float> elems){
	    final int N = elems.size();  // For brevity, inline if you wish
	    return (N == 0) ? 0 : (myAverage(elems.subList(1,N)) * (N-1) + elems.get(0)) / N;
	}
 
	public static void main (String[] args) throws java.lang.Exception
	{
		List<Float> list = new ArrayList<Float>();
		list.add(4.0f);
		list.add(7.0f);
		list.add(12.0f);
		list.add(3.0f);
 
		System.out.println(myAverage(list));
	}
}

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