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.function.LongConsumer; 29 import java.util.stream.Collector; 30 31 /** 32 * A state object for collecting statistics such as count, min, max, sum, and 33 * average. 34 * 35 * <p>This class is designed to work with (though does not require) 36 * {@linkplain java.util.stream streams}. For example, you can compute 37 * summary statistics on a stream of longs with: 38 * <pre> {@code 39 * LongSummaryStatistics stats = longStream.collect(LongSummaryStatistics::new, 40 * LongSummaryStatistics::accept, 41 * LongSummaryStatistics::combine); 42 * }</pre> 43 * 44 * <p>{@code LongSummaryStatistics} can be used as a 45 * {@linkplain java.util.stream.Stream#collect(Collector) reduction} 46 * target for a {@linkplain java.util.stream.Stream stream}. For example: 47 * 48 * <pre> {@code 49 * LongSummaryStatistics stats = people.stream() 50 * .collect(Collectors.summarizingLong(Person::getAge)); 51 *}</pre> 52 * 53 * This computes, in a single pass, the count of people, as well as the minimum, 54 * maximum, sum, and average of their ages. 55 * 56 * @implNote This implementation is not thread safe. However, it is safe to use 57 * {@link java.util.stream.Collectors#summarizingLong(java.util.function.ToLongFunction) 58 * Collectors.summarizingLong()} on a parallel stream, because the parallel 59 * implementation of {@link java.util.stream.Stream#collect Stream.collect()} 60 * provides the necessary partitioning, isolation, and merging of results for 61 * safe and efficient parallel execution. 62 * 63 * <p>This implementation does not check for overflow of the count or the sum. 64 * @since 1.8 65 */ 66 @SuppressWarnings("overloads") 67 public class LongSummaryStatistics implements LongConsumer, IntConsumer { 68 private long count; 69 private long sum; 70 private long min = Long.MAX_VALUE; 71 private long max = Long.MIN_VALUE; 72 73 /** 74 * Constructs an empty instance with zero count, zero sum, 75 * {@code Long.MAX_VALUE} min, {@code Long.MIN_VALUE} max and zero 76 * average. 77 */ LongSummaryStatistics()78 public LongSummaryStatistics() { } 79 80 /** 81 * Constructs a non-empty instance with the specified {@code count}, 82 * {@code min}, {@code max}, and {@code sum}. 83 * 84 * <p>If {@code count} is zero then the remaining arguments are ignored and 85 * an empty instance is constructed. 86 * 87 * <p>If the arguments are inconsistent then an {@code IllegalArgumentException} 88 * is thrown. The necessary consistent argument conditions are: 89 * <ul> 90 * <li>{@code count >= 0}</li> 91 * <li>{@code min <= max}</li> 92 * </ul> 93 * @apiNote 94 * The enforcement of argument correctness means that the retrieved set of 95 * recorded values obtained from a {@code LongSummaryStatistics} source 96 * instance may not be a legal set of arguments for this constructor due to 97 * arithmetic overflow of the source's recorded count of values. 98 * The consistent argument conditions are not sufficient to prevent the 99 * creation of an internally inconsistent instance. An example of such a 100 * state would be an instance with: {@code count} = 2, {@code min} = 1, 101 * {@code max} = 2, and {@code sum} = 0. 102 * 103 * @param count the count of values 104 * @param min the minimum value 105 * @param max the maximum value 106 * @param sum the sum of all values 107 * @throws IllegalArgumentException if the arguments are inconsistent 108 * @since 10 109 */ LongSummaryStatistics(long count, long min, long max, long sum)110 public LongSummaryStatistics(long count, long min, long max, long sum) 111 throws IllegalArgumentException { 112 if (count < 0L) { 113 throw new IllegalArgumentException("Negative count value"); 114 } else if (count > 0L) { 115 if (min > max) throw new IllegalArgumentException("Minimum greater than maximum"); 116 117 this.count = count; 118 this.sum = sum; 119 this.min = min; 120 this.max = max; 121 } 122 // Use default field values if count == 0 123 } 124 125 /** 126 * Records a new {@code int} value into the summary information. 127 * 128 * @param value the input value 129 */ 130 @Override accept(int value)131 public void accept(int value) { 132 accept((long) value); 133 } 134 135 /** 136 * Records a new {@code long} value into the summary information. 137 * 138 * @param value the input value 139 */ 140 @Override accept(long value)141 public void accept(long value) { 142 ++count; 143 sum += value; 144 min = Math.min(min, value); 145 max = Math.max(max, value); 146 } 147 148 /** 149 * Combines the state of another {@code LongSummaryStatistics} into this 150 * one. 151 * 152 * @param other another {@code LongSummaryStatistics} 153 * @throws NullPointerException if {@code other} is null 154 */ combine(LongSummaryStatistics other)155 public void combine(LongSummaryStatistics other) { 156 count += other.count; 157 sum += other.sum; 158 min = Math.min(min, other.min); 159 max = Math.max(max, other.max); 160 } 161 162 /** 163 * Returns the count of values recorded. 164 * 165 * @return the count of values 166 */ getCount()167 public final long getCount() { 168 return count; 169 } 170 171 /** 172 * Returns the sum of values recorded, or zero if no values have been 173 * recorded. 174 * 175 * @return the sum of values, or zero if none 176 */ getSum()177 public final long getSum() { 178 return sum; 179 } 180 181 /** 182 * Returns the minimum value recorded, or {@code Long.MAX_VALUE} if no 183 * values have been recorded. 184 * 185 * @return the minimum value, or {@code Long.MAX_VALUE} if none 186 */ getMin()187 public final long getMin() { 188 return min; 189 } 190 191 /** 192 * Returns the maximum value recorded, or {@code Long.MIN_VALUE} if no 193 * values have been recorded 194 * 195 * @return the maximum value, or {@code Long.MIN_VALUE} if none 196 */ getMax()197 public final long getMax() { 198 return max; 199 } 200 201 /** 202 * Returns the arithmetic mean of values recorded, or zero if no values have been 203 * recorded. 204 * 205 * @return The arithmetic mean of values, or zero if none 206 */ getAverage()207 public final double getAverage() { 208 return getCount() > 0 ? (double) getSum() / getCount() : 0.0d; 209 } 210 211 /** 212 * Returns a non-empty string representation of this object suitable for 213 * debugging. The exact presentation format is unspecified and may vary 214 * between implementations and versions. 215 */ 216 @Override toString()217 public String toString() { 218 return String.format( 219 "%s{count=%d, sum=%d, min=%d, average=%f, max=%d}", 220 this.getClass().getSimpleName(), 221 getCount(), 222 getSum(), 223 getMin(), 224 getAverage(), 225 getMax()); 226 } 227 } 228