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 29 /** 30 * A state object for collecting statistics such as count, min, max, sum, and 31 * average. 32 * 33 * <p>This class is designed to work with (though does not require) 34 * {@linkplain java.util.stream streams}. For example, you can compute 35 * summary statistics on a stream of ints with: 36 * <pre> {@code 37 * IntSummaryStatistics stats = intStream.collect(IntSummaryStatistics::new, 38 * IntSummaryStatistics::accept, 39 * IntSummaryStatistics::combine); 40 * }</pre> 41 * 42 * <p>{@code IntSummaryStatistics} can be used as a 43 * {@linkplain java.util.stream.Stream#collect(Collector) reduction} 44 * target for a {@linkplain java.util.stream.Stream stream}. For example: 45 * 46 * <pre> {@code 47 * IntSummaryStatistics stats = people.stream() 48 * .collect(Collectors.summarizingInt(Person::getDependents)); 49 *}</pre> 50 * 51 * This computes, in a single pass, the count of people, as well as the minimum, 52 * maximum, sum, and average of their number of dependents. 53 * 54 * @implNote This implementation is not thread safe. However, it is safe to use 55 * {@link java.util.stream.Collectors#summarizingInt(java.util.function.ToIntFunction) 56 * Collectors.toIntStatistics()} on a parallel stream, because the parallel 57 * implementation of {@link java.util.stream.Stream#collect Stream.collect()} 58 * provides the necessary partitioning, isolation, and merging of results for 59 * safe and efficient parallel execution. 60 * 61 * <p>This implementation does not check for overflow of the sum. 62 * @since 1.8 63 */ 64 public class IntSummaryStatistics implements IntConsumer { 65 private long count; 66 private long sum; 67 private int min = Integer.MAX_VALUE; 68 private int max = Integer.MIN_VALUE; 69 70 /** 71 * Construct an empty instance with zero count, zero sum, 72 * {@code Integer.MAX_VALUE} min, {@code Integer.MIN_VALUE} max and zero 73 * average. 74 */ IntSummaryStatistics()75 public IntSummaryStatistics() { } 76 77 /** 78 * Records a new value into the summary information 79 * 80 * @param value the input value 81 */ 82 @Override accept(int value)83 public void accept(int value) { 84 ++count; 85 sum += value; 86 min = Math.min(min, value); 87 max = Math.max(max, value); 88 } 89 90 /** 91 * Combines the state of another {@code IntSummaryStatistics} into this one. 92 * 93 * @param other another {@code IntSummaryStatistics} 94 * @throws NullPointerException if {@code other} is null 95 */ combine(IntSummaryStatistics other)96 public void combine(IntSummaryStatistics other) { 97 count += other.count; 98 sum += other.sum; 99 min = Math.min(min, other.min); 100 max = Math.max(max, other.max); 101 } 102 103 /** 104 * Returns the count of values recorded. 105 * 106 * @return the count of values 107 */ getCount()108 public final long getCount() { 109 return count; 110 } 111 112 /** 113 * Returns the sum of values recorded, or zero if no values have been 114 * recorded. 115 * 116 * @return the sum of values, or zero if none 117 */ getSum()118 public final long getSum() { 119 return sum; 120 } 121 122 /** 123 * Returns the minimum value recorded, or {@code Integer.MAX_VALUE} if no 124 * values have been recorded. 125 * 126 * @return the minimum value, or {@code Integer.MAX_VALUE} if none 127 */ getMin()128 public final int getMin() { 129 return min; 130 } 131 132 /** 133 * Returns the maximum value recorded, or {@code Integer.MIN_VALUE} if no 134 * values have been recorded. 135 * 136 * @return the maximum value, or {@code Integer.MIN_VALUE} if none 137 */ getMax()138 public final int getMax() { 139 return max; 140 } 141 142 /** 143 * Returns the arithmetic mean of values recorded, or zero if no values have been 144 * recorded. 145 * 146 * @return the arithmetic mean of values, or zero if none 147 */ getAverage()148 public final double getAverage() { 149 return getCount() > 0 ? (double) getSum() / getCount() : 0.0d; 150 } 151 152 @Override 153 /** 154 * {@inheritDoc} 155 * 156 * Returns a non-empty string representation of this object suitable for 157 * debugging. The exact presentation format is unspecified and may vary 158 * between implementations and versions. 159 */ toString()160 public String toString() { 161 return String.format( 162 "%s{count=%d, sum=%d, min=%d, average=%f, max=%d}", 163 this.getClass().getSimpleName(), 164 getCount(), 165 getSum(), 166 getMin(), 167 getAverage(), 168 getMax()); 169 } 170 } 171