1 /* 2 * Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ 25 package java.util; 26 27 import java.util.function.IntConsumer; 28 import java.util.stream.Collector; 29 30 /** 31 * A state object for collecting statistics such as count, min, max, sum, and 32 * average. 33 * 34 * <p>This class is designed to work with (though does not require) 35 * {@linkplain java.util.stream streams}. For example, you can compute 36 * summary statistics on a stream of ints with: 37 * <pre> {@code 38 * IntSummaryStatistics stats = intStream.collect(IntSummaryStatistics::new, 39 * IntSummaryStatistics::accept, 40 * IntSummaryStatistics::combine); 41 * }</pre> 42 * 43 * <p>{@code IntSummaryStatistics} can be used as a 44 * {@linkplain java.util.stream.Stream#collect(Collector) reduction} 45 * target for a {@linkplain java.util.stream.Stream stream}. For example: 46 * 47 * <pre> {@code 48 * IntSummaryStatistics stats = people.stream() 49 * .collect(Collectors.summarizingInt(Person::getDependents)); 50 *}</pre> 51 * 52 * This computes, in a single pass, the count of people, as well as the minimum, 53 * maximum, sum, and average of their number of dependents. 54 * 55 * @implNote This implementation is not thread safe. However, it is safe to use 56 * {@link java.util.stream.Collectors#summarizingInt(java.util.function.ToIntFunction) 57 * Collectors.toIntStatistics()} on a parallel stream, because the parallel 58 * implementation of {@link java.util.stream.Stream#collect Stream.collect()} 59 * provides the necessary partitioning, isolation, and merging of results for 60 * safe and efficient parallel execution. 61 * 62 * <p>This implementation does not check for overflow of the sum. 63 * @since 1.8 64 */ 65 public class IntSummaryStatistics implements IntConsumer { 66 private long count; 67 private long sum; 68 private int min = Integer.MAX_VALUE; 69 private int max = Integer.MIN_VALUE; 70 71 /** 72 * Construct an empty instance with zero count, zero sum, 73 * {@code Integer.MAX_VALUE} min, {@code Integer.MIN_VALUE} max and zero 74 * average. 75 */ IntSummaryStatistics()76 public IntSummaryStatistics() { } 77 78 /** 79 * Records a new value into the summary information 80 * 81 * @param value the input value 82 */ 83 @Override accept(int value)84 public void accept(int value) { 85 ++count; 86 sum += value; 87 min = Math.min(min, value); 88 max = Math.max(max, value); 89 } 90 91 /** 92 * Combines the state of another {@code IntSummaryStatistics} into this one. 93 * 94 * @param other another {@code IntSummaryStatistics} 95 * @throws NullPointerException if {@code other} is null 96 */ combine(IntSummaryStatistics other)97 public void combine(IntSummaryStatistics other) { 98 count += other.count; 99 sum += other.sum; 100 min = Math.min(min, other.min); 101 max = Math.max(max, other.max); 102 } 103 104 /** 105 * Returns the count of values recorded. 106 * 107 * @return the count of values 108 */ getCount()109 public final long getCount() { 110 return count; 111 } 112 113 /** 114 * Returns the sum of values recorded, or zero if no values have been 115 * recorded. 116 * 117 * @return the sum of values, or zero if none 118 */ getSum()119 public final long getSum() { 120 return sum; 121 } 122 123 /** 124 * Returns the minimum value recorded, or {@code Integer.MAX_VALUE} if no 125 * values have been recorded. 126 * 127 * @return the minimum value, or {@code Integer.MAX_VALUE} if none 128 */ getMin()129 public final int getMin() { 130 return min; 131 } 132 133 /** 134 * Returns the maximum value recorded, or {@code Integer.MIN_VALUE} if no 135 * values have been recorded. 136 * 137 * @return the maximum value, or {@code Integer.MIN_VALUE} if none 138 */ getMax()139 public final int getMax() { 140 return max; 141 } 142 143 /** 144 * Returns the arithmetic mean of values recorded, or zero if no values have been 145 * recorded. 146 * 147 * @return the arithmetic mean of values, or zero if none 148 */ getAverage()149 public final double getAverage() { 150 return getCount() > 0 ? (double) getSum() / getCount() : 0.0d; 151 } 152 153 @Override 154 /** 155 * {@inheritDoc} 156 * 157 * Returns a non-empty string representation of this object suitable for 158 * debugging. The exact presentation format is unspecified and may vary 159 * between implementations and versions. 160 */ toString()161 public String toString() { 162 return String.format( 163 "%s{count=%d, sum=%d, min=%d, average=%f, max=%d}", 164 this.getClass().getSimpleName(), 165 getCount(), 166 getSum(), 167 getMin(), 168 getAverage(), 169 getMax()); 170 } 171 } 172