package com.wrox.algorithms.iteration;/** * A {@link PowerCalculator} that uses recursion. * */public final class RecursivePowerCalculator implements PowerCalculator {    /** The single, publicly accessible, instance of the comparator. */    public static final RecursivePowerCalculator INSTANCE = new RecursivePowerCalculator();    /**     * Constructor marked private to prevent instantiation.     */    private RecursivePowerCalculator() {    }    public int calculate(int base, int exponent) {        assert exponent >= 0 : "exponent can't be < 0";        return exponent > 0 ? base * calculate(base, exponent - 1) : 1;    }}