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 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.toLongStatistics()} 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 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 * Construct 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 * Records a new {@code int} value into the summary information. 81 * 82 * @param value the input value 83 */ 84 @Override accept(int value)85 public void accept(int value) { 86 accept((long) value); 87 } 88 89 /** 90 * Records a new {@code long} value into the summary information. 91 * 92 * @param value the input value 93 */ 94 @Override accept(long value)95 public void accept(long value) { 96 ++count; 97 sum += value; 98 min = Math.min(min, value); 99 max = Math.max(max, value); 100 } 101 102 /** 103 * Combines the state of another {@code LongSummaryStatistics} into this 104 * one. 105 * 106 * @param other another {@code LongSummaryStatistics} 107 * @throws NullPointerException if {@code other} is null 108 */ combine(LongSummaryStatistics other)109 public void combine(LongSummaryStatistics other) { 110 count += other.count; 111 sum += other.sum; 112 min = Math.min(min, other.min); 113 max = Math.max(max, other.max); 114 } 115 116 /** 117 * Returns the count of values recorded. 118 * 119 * @return the count of values 120 */ getCount()121 public final long getCount() { 122 return count; 123 } 124 125 /** 126 * Returns the sum of values recorded, or zero if no values have been 127 * recorded. 128 * 129 * @return the sum of values, or zero if none 130 */ getSum()131 public final long getSum() { 132 return sum; 133 } 134 135 /** 136 * Returns the minimum value recorded, or {@code Long.MAX_VALUE} if no 137 * values have been recorded. 138 * 139 * @return the minimum value, or {@code Long.MAX_VALUE} if none 140 */ getMin()141 public final long getMin() { 142 return min; 143 } 144 145 /** 146 * Returns the maximum value recorded, or {@code Long.MIN_VALUE} if no 147 * values have been recorded 148 * 149 * @return the maximum value, or {@code Long.MIN_VALUE} if none 150 */ getMax()151 public final long getMax() { 152 return max; 153 } 154 155 /** 156 * Returns the arithmetic mean of values recorded, or zero if no values have been 157 * recorded. 158 * 159 * @return The arithmetic mean of values, or zero if none 160 */ getAverage()161 public final double getAverage() { 162 return getCount() > 0 ? (double) getSum() / getCount() : 0.0d; 163 } 164 165 @Override 166 /** 167 * {@inheritDoc} 168 * 169 * Returns a non-empty string representation of this object suitable for 170 * debugging. The exact presentation format is unspecified and may vary 171 * between implementations and versions. 172 */ toString()173 public String toString() { 174 return String.format( 175 "%s{count=%d, sum=%d, min=%d, average=%f, max=%d}", 176 this.getClass().getSimpleName(), 177 getCount(), 178 getSum(), 179 getMin(), 180 getAverage(), 181 getMax()); 182 } 183 } 184