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 public class LongSummaryStatistics implements LongConsumer, IntConsumer { 67 private long count; 68 private long sum; 69 private long min = Long.MAX_VALUE; 70 private long max = Long.MIN_VALUE; 71 72 /** 73 * Constructs an empty instance with zero count, zero sum, 74 * {@code Long.MAX_VALUE} min, {@code Long.MIN_VALUE} max and zero 75 * average. 76 */ LongSummaryStatistics()77 public LongSummaryStatistics() { } 78 79 /** 80 * Constructs a non-empty instance with the specified {@code count}, 81 * {@code min}, {@code max}, and {@code sum}. 82 * 83 * <p>If {@code count} is zero then the remaining arguments are ignored and 84 * an empty instance is constructed. 85 * 86 * <p>If the arguments are inconsistent then an {@code IllegalArgumentException} 87 * is thrown. The necessary consistent argument conditions are: 88 * <ul> 89 * <li>{@code count >= 0}</li> 90 * <li>{@code min <= max}</li> 91 * </ul> 92 * @apiNote 93 * The enforcement of argument correctness means that the retrieved set of 94 * recorded values obtained from a {@code LongSummaryStatistics} source 95 * instance may not be a legal set of arguments for this constructor due to 96 * arithmetic overflow of the source's recorded count of values. 97 * The consistent argument conditions are not sufficient to prevent the 98 * creation of an internally inconsistent instance. An example of such a 99 * state would be an instance with: {@code count} = 2, {@code min} = 1, 100 * {@code max} = 2, and {@code sum} = 0. 101 * 102 * @param count the count of values 103 * @param min the minimum value 104 * @param max the maximum value 105 * @param sum the sum of all values 106 * @throws IllegalArgumentException if the arguments are inconsistent 107 * @since 10 108 */ LongSummaryStatistics(long count, long min, long max, long sum)109 public LongSummaryStatistics(long count, long min, long max, long sum) 110 throws IllegalArgumentException { 111 if (count < 0L) { 112 throw new IllegalArgumentException("Negative count value"); 113 } else if (count > 0L) { 114 if (min > max) throw new IllegalArgumentException("Minimum greater than maximum"); 115 116 this.count = count; 117 this.sum = sum; 118 this.min = min; 119 this.max = max; 120 } 121 // Use default field values if count == 0 122 } 123 124 /** 125 * Records a new {@code int} value into the summary information. 126 * 127 * @param value the input value 128 */ 129 @Override accept(int value)130 public void accept(int value) { 131 accept((long) value); 132 } 133 134 /** 135 * Records a new {@code long} value into the summary information. 136 * 137 * @param value the input value 138 */ 139 @Override accept(long value)140 public void accept(long value) { 141 ++count; 142 sum += value; 143 min = Math.min(min, value); 144 max = Math.max(max, value); 145 } 146 147 /** 148 * Combines the state of another {@code LongSummaryStatistics} into this 149 * one. 150 * 151 * @param other another {@code LongSummaryStatistics} 152 * @throws NullPointerException if {@code other} is null 153 */ combine(LongSummaryStatistics other)154 public void combine(LongSummaryStatistics other) { 155 count += other.count; 156 sum += other.sum; 157 min = Math.min(min, other.min); 158 max = Math.max(max, other.max); 159 } 160 161 /** 162 * Returns the count of values recorded. 163 * 164 * @return the count of values 165 */ getCount()166 public final long getCount() { 167 return count; 168 } 169 170 /** 171 * Returns the sum of values recorded, or zero if no values have been 172 * recorded. 173 * 174 * @return the sum of values, or zero if none 175 */ getSum()176 public final long getSum() { 177 return sum; 178 } 179 180 /** 181 * Returns the minimum value recorded, or {@code Long.MAX_VALUE} if no 182 * values have been recorded. 183 * 184 * @return the minimum value, or {@code Long.MAX_VALUE} if none 185 */ getMin()186 public final long getMin() { 187 return min; 188 } 189 190 /** 191 * Returns the maximum value recorded, or {@code Long.MIN_VALUE} if no 192 * values have been recorded 193 * 194 * @return the maximum value, or {@code Long.MIN_VALUE} if none 195 */ getMax()196 public final long getMax() { 197 return max; 198 } 199 200 /** 201 * Returns the arithmetic mean of values recorded, or zero if no values have been 202 * recorded. 203 * 204 * @return The arithmetic mean of values, or zero if none 205 */ getAverage()206 public final double getAverage() { 207 return getCount() > 0 ? (double) getSum() / getCount() : 0.0d; 208 } 209 210 /** 211 * Returns a non-empty string representation of this object suitable for 212 * debugging. The exact presentation format is unspecified and may vary 213 * between implementations and versions. 214 */ 215 @Override toString()216 public String toString() { 217 return String.format( 218 "%s{count=%d, sum=%d, min=%d, average=%f, max=%d}", 219 this.getClass().getSimpleName(), 220 getCount(), 221 getSum(), 222 getMin(), 223 getAverage(), 224 getMax()); 225 } 226 } 227