Java tutorial
/* * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You under the Apache License, Version 2.0 * (the "License"); you may not use this file except in compliance with * the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.apache.commons.math.stat.descriptive.summary; import java.io.Serializable; import org.apache.commons.math.stat.descriptive.AbstractStorelessUnivariateStatistic; /** * Returns the sum of the available values. * <p> * If there are no values in the dataset, or any of the values are * <code>NaN</code>, then <code>NaN</code> is returned.</p> * <p> * <strong>Note that this implementation is not synchronized.</strong> If * multiple threads access an instance of this class concurrently, and at least * one of the threads invokes the <code>increment()</code> or * <code>clear()</code> method, it must be synchronized externally.</p> * * @version $Revision: 1006299 $ $Date: 2010-10-10 16:47:17 +0200 (dim. 10 oct. 2010) $ */ public class Sum extends AbstractStorelessUnivariateStatistic implements Serializable { /** Serializable version identifier */ private static final long serialVersionUID = -8231831954703408316L; /** */ private long n; /** * The currently running sum. */ private double value; /** * Create a Sum instance */ public Sum() { n = 0; value = Double.NaN; } /** * Copy constructor, creates a new {@code Sum} identical * to the {@code original} * * @param original the {@code Sum} instance to copy */ public Sum(Sum original) { copy(original, this); } /** * {@inheritDoc} */ @Override public void increment(final double d) { if (n == 0) { value = d; } else { value += d; } n++; } /** * {@inheritDoc} */ @Override public double getResult() { return value; } /** * {@inheritDoc} */ public long getN() { return n; } /** * {@inheritDoc} */ @Override public void clear() { value = Double.NaN; n = 0; } /** * The sum of the entries in the specified portion of * the input array, or <code>Double.NaN</code> if the designated subarray * is empty. * <p> * Throws <code>IllegalArgumentException</code> if the array is null.</p> * * @param values the input array * @param begin index of the first array element to include * @param length the number of elements to include * @return the sum of the values or Double.NaN if length = 0 * @throws IllegalArgumentException if the array is null or the array index * parameters are not valid */ @Override public double evaluate(final double[] values, final int begin, final int length) { double sum = Double.NaN; if (test(values, begin, length)) { sum = 0.0; for (int i = begin; i < begin + length; i++) { sum += values[i]; } } return sum; } /** * The weighted sum of the entries in the specified portion of * the input array, or <code>Double.NaN</code> if the designated subarray * is empty. * <p> * Throws <code>IllegalArgumentException</code> if any of the following are true: * <ul><li>the values array is null</li> * <li>the weights array is null</li> * <li>the weights array does not have the same length as the values array</li> * <li>the weights array contains one or more infinite values</li> * <li>the weights array contains one or more NaN values</li> * <li>the weights array contains negative values</li> * <li>the start and length arguments do not determine a valid array</li> * </ul></p> * <p> * Uses the formula, <pre> * weighted sum = Σ(values[i] * weights[i]) * </pre></p> * * @param values the input array * @param weights the weights array * @param begin index of the first array element to include * @param length the number of elements to include * @return the sum of the values or Double.NaN if length = 0 * @throws IllegalArgumentException if the parameters are not valid * @since 2.1 */ public double evaluate(final double[] values, final double[] weights, final int begin, final int length) { double sum = Double.NaN; if (test(values, weights, begin, length)) { sum = 0.0; for (int i = begin; i < begin + length; i++) { sum += values[i] * weights[i]; } } return sum; } /** * The weighted sum of the entries in the the input array. * <p> * Throws <code>IllegalArgumentException</code> if any of the following are true: * <ul><li>the values array is null</li> * <li>the weights array is null</li> * <li>the weights array does not have the same length as the values array</li> * <li>the weights array contains one or more infinite values</li> * <li>the weights array contains one or more NaN values</li> * <li>the weights array contains negative values</li> * </ul></p> * <p> * Uses the formula, <pre> * weighted sum = Σ(values[i] * weights[i]) * </pre></p> * * @param values the input array * @param weights the weights array * @return the sum of the values or Double.NaN if length = 0 * @throws IllegalArgumentException if the parameters are not valid * @since 2.1 */ public double evaluate(final double[] values, final double[] weights) { return evaluate(values, weights, 0, values.length); } /** * {@inheritDoc} */ @Override public Sum copy() { Sum result = new Sum(); copy(this, result); return result; } /** * Copies source to dest. * <p>Neither source nor dest can be null.</p> * * @param source Sum to copy * @param dest Sum to copy to * @throws NullPointerException if either source or dest is null */ public static void copy(Sum source, Sum dest) { dest.setData(source.getDataRef()); dest.n = source.n; dest.value = source.value; } }