/* * Copyright (c) 2000 David Flanagan.  All rights reserved. * This code is from the book Java Examples in a Nutshell, 2nd Edition. * It is provided AS-IS, WITHOUT ANY WARRANTY either expressed or implied. * You may study, use, and modify it for any non-commercial purpose. * You may distribute it non-commercially as long as you retain this notice. * For a commercial use license, or to purchase the book (recommended), * visit http://www.davidflanagan.com/javaexamples2. */package com.davidflanagan.examples.classes;/** * A class to compute the running average of numbers passed to it **/public class Averager {    // Private fields to hold the current state.    private int n = 0;    private double sum = 0.0, sumOfSquares = 0.0;    /**      * This method adds a new datum into the average.     **/    public void addDatum(double x) {        n++;        sum += x;        sumOfSquares += x * x;    }        /** This method returns the average of all numbers passed to addDatum() */    public double getAverage() { return sum / n; }    /** This method returns the standard deviation of the data */    public double getStandardDeviation() {          return Math.sqrt(((sumOfSquares - sum*sum/n)/n));    }    /** This method returns the number of numbers passed to addDatum() */    public double getNum() { return n; }    /** This method returns the sum of all numbers passed to addDatum() */    public double getSum() { return sum; }    /** This method returns the sum of the squares of all numbers. */    public double getSumOfSquares() { return sumOfSquares; }    /** This method resets the Averager object to begin from scratch */    public void reset() { n = 0; sum = 0.0; sumOfSquares = 0.0; }    /**      * This nested class is a simple test program we can use to check that      * our code works okay.     **/    public static class Test {        public static void main(String args[]) {            Averager a = new Averager();            for(int i = 1; i <= 100; i++) a.addDatum(i);            System.out.println("Average: " + a.getAverage());            System.out.println("Standard Deviation: " +			       a.getStandardDeviation());            System.out.println("N: " + a.getNum());            System.out.println("Sum: " + a.getSum());            System.out.println("Sum of squares: " + a.getSumOfSquares());        }    }}