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.function.LongConsumer; 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 longs with: 37 * <pre> {@code 38 * LongSummaryStatistics stats = longStream.collect(LongSummaryStatistics::new, 39 * LongSummaryStatistics::accept, 40 * LongSummaryStatistics::combine); 41 * }</pre> 42 * 43 * <p>{@code LongSummaryStatistics} 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 * LongSummaryStatistics stats = people.stream() 49 * .collect(Collectors.summarizingLong(Person::getAge)); 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 ages. 54 * 55 * @implNote This implementation is not thread safe. However, it is safe to use 56 * {@link java.util.stream.Collectors#summarizingLong(java.util.function.ToLongFunction) 57 * Collectors.toLongStatistics()} 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 LongSummaryStatistics implements LongConsumer, IntConsumer { 66 private long count; 67 private long sum; 68 private long min = Long.MAX_VALUE; 69 private long max = Long.MIN_VALUE; 70 71 /** 72 * Construct an empty instance with zero count, zero sum, 73 * {@code Long.MAX_VALUE} min, {@code Long.MIN_VALUE} max and zero 74 * average. 75 */ LongSummaryStatistics()76 public LongSummaryStatistics() { } 77 78 /** 79 * Records a new {@code int} 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 accept((long) value); 86 } 87 88 /** 89 * Records a new {@code long} value into the summary information. 90 * 91 * @param value the input value 92 */ 93 @Override accept(long value)94 public void accept(long value) { 95 ++count; 96 sum += value; 97 min = Math.min(min, value); 98 max = Math.max(max, value); 99 } 100 101 /** 102 * Combines the state of another {@code LongSummaryStatistics} into this 103 * one. 104 * 105 * @param other another {@code LongSummaryStatistics} 106 * @throws NullPointerException if {@code other} is null 107 */ combine(LongSummaryStatistics other)108 public void combine(LongSummaryStatistics other) { 109 count += other.count; 110 sum += other.sum; 111 min = Math.min(min, other.min); 112 max = Math.max(max, other.max); 113 } 114 115 /** 116 * Returns the count of values recorded. 117 * 118 * @return the count of values 119 */ getCount()120 public final long getCount() { 121 return count; 122 } 123 124 /** 125 * Returns the sum of values recorded, or zero if no values have been 126 * recorded. 127 * 128 * @return the sum of values, or zero if none 129 */ getSum()130 public final long getSum() { 131 return sum; 132 } 133 134 /** 135 * Returns the minimum value recorded, or {@code Long.MAX_VALUE} if no 136 * values have been recorded. 137 * 138 * @return the minimum value, or {@code Long.MAX_VALUE} if none 139 */ getMin()140 public final long getMin() { 141 return min; 142 } 143 144 /** 145 * Returns the maximum value recorded, or {@code Long.MIN_VALUE} if no 146 * values have been recorded 147 * 148 * @return the maximum value, or {@code Long.MIN_VALUE} if none 149 */ getMax()150 public final long getMax() { 151 return max; 152 } 153 154 /** 155 * Returns the arithmetic mean of values recorded, or zero if no values have been 156 * recorded. 157 * 158 * @return The arithmetic mean of values, or zero if none 159 */ getAverage()160 public final double getAverage() { 161 return getCount() > 0 ? (double) getSum() / getCount() : 0.0d; 162 } 163 164 @Override 165 /** 166 * {@inheritDoc} 167 * 168 * Returns a non-empty string representation of this object suitable for 169 * debugging. The exact presentation format is unspecified and may vary 170 * between implementations and versions. 171 */ toString()172 public String toString() { 173 return String.format( 174 "%s{count=%d, sum=%d, min=%d, average=%f, max=%d}", 175 this.getClass().getSimpleName(), 176 getCount(), 177 getSum(), 178 getMin(), 179 getAverage(), 180 getMax()); 181 } 182 } 183