/**
 * Defines an interface that keeps track of a statistic
 * about a stream of numbers.
 */
public interface Statistic {
    /**
     * Provide a name describing the statistic.
     * @return the name of this statistic
     */
    String getName();
    /**
     * Provide the current statistic value.
     * @return the current statistic value.
     */
    double getValue();
    /**
     * Update the statistic value given a new observation.
     * @param x a new observation
     */
    void update(double x);
}