1 /* 2 * Copyright (c) 2012, 2019, 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.summarizingInt()} 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 count or 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 * Constructs 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 * Constructs a non-empty instance with the specified {@code count}, 80 * {@code min}, {@code max}, and {@code sum}. 81 * 82 * <p>If {@code count} is zero then the remaining arguments are ignored and 83 * an empty instance is constructed. 84 * 85 * <p>If the arguments are inconsistent then an {@code IllegalArgumentException} 86 * is thrown. The necessary consistent argument conditions are: 87 * <ul> 88 * <li>{@code count >= 0}</li> 89 * <li>{@code min <= max}</li> 90 * </ul> 91 * @apiNote 92 * The enforcement of argument correctness means that the retrieved set of 93 * recorded values obtained from a {@code IntSummaryStatistics} source 94 * instance may not be a legal set of arguments for this constructor due to 95 * arithmetic overflow of the source's recorded count of values. 96 * The consistent argument conditions are not sufficient to prevent the 97 * creation of an internally inconsistent instance. An example of such a 98 * state would be an instance with: {@code count} = 2, {@code min} = 1, 99 * {@code max} = 2, and {@code sum} = 0. 100 * 101 * @param count the count of values 102 * @param min the minimum value 103 * @param max the maximum value 104 * @param sum the sum of all values 105 * @throws IllegalArgumentException if the arguments are inconsistent 106 * @since 10 107 */ IntSummaryStatistics(long count, int min, int max, long sum)108 public IntSummaryStatistics(long count, int min, int max, long sum) 109 throws IllegalArgumentException { 110 if (count < 0L) { 111 throw new IllegalArgumentException("Negative count value"); 112 } else if (count > 0L) { 113 if (min > max) throw new IllegalArgumentException("Minimum greater than maximum"); 114 115 this.count = count; 116 this.sum = sum; 117 this.min = min; 118 this.max = max; 119 } 120 // Use default field values if count == 0 121 } 122 123 /** 124 * Records a new value into the summary information 125 * 126 * @param value the input value 127 */ 128 @Override accept(int value)129 public void accept(int value) { 130 ++count; 131 sum += value; 132 min = Math.min(min, value); 133 max = Math.max(max, value); 134 } 135 136 /** 137 * Combines the state of another {@code IntSummaryStatistics} into this one. 138 * 139 * @param other another {@code IntSummaryStatistics} 140 * @throws NullPointerException if {@code other} is null 141 */ combine(IntSummaryStatistics other)142 public void combine(IntSummaryStatistics other) { 143 count += other.count; 144 sum += other.sum; 145 min = Math.min(min, other.min); 146 max = Math.max(max, other.max); 147 } 148 149 /** 150 * Returns the count of values recorded. 151 * 152 * @return the count of values 153 */ getCount()154 public final long getCount() { 155 return count; 156 } 157 158 /** 159 * Returns the sum of values recorded, or zero if no values have been 160 * recorded. 161 * 162 * @return the sum of values, or zero if none 163 */ getSum()164 public final long getSum() { 165 return sum; 166 } 167 168 /** 169 * Returns the minimum value recorded, or {@code Integer.MAX_VALUE} if no 170 * values have been recorded. 171 * 172 * @return the minimum value, or {@code Integer.MAX_VALUE} if none 173 */ getMin()174 public final int getMin() { 175 return min; 176 } 177 178 /** 179 * Returns the maximum value recorded, or {@code Integer.MIN_VALUE} if no 180 * values have been recorded. 181 * 182 * @return the maximum value, or {@code Integer.MIN_VALUE} if none 183 */ getMax()184 public final int getMax() { 185 return max; 186 } 187 188 /** 189 * Returns the arithmetic mean of values recorded, or zero if no values have been 190 * recorded. 191 * 192 * @return the arithmetic mean of values, or zero if none 193 */ getAverage()194 public final double getAverage() { 195 return getCount() > 0 ? (double) getSum() / getCount() : 0.0d; 196 } 197 198 /** 199 * Returns a non-empty string representation of this object suitable for 200 * debugging. The exact presentation format is unspecified and may vary 201 * between implementations and versions. 202 */ 203 @Override toString()204 public String toString() { 205 return String.format( 206 "%s{count=%d, sum=%d, min=%d, average=%f, max=%d}", 207 this.getClass().getSimpleName(), 208 getCount(), 209 getSum(), 210 getMin(), 211 getAverage(), 212 getMax()); 213 } 214 } 215