Java tutorial
/* * Copyright (c) 2012, 2017, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package java.util; import java.util.function.IntConsumer; import java.util.function.LongConsumer; import java.util.stream.Collector; /** * A state object for collecting statistics such as count, min, max, sum, and * average. * * <p>This class is designed to work with (though does not require) * {@linkplain java.util.stream streams}. For example, you can compute * summary statistics on a stream of longs with: * <pre> {@code * LongSummaryStatistics stats = longStream.collect(LongSummaryStatistics::new, * LongSummaryStatistics::accept, * LongSummaryStatistics::combine); * }</pre> * * <p>{@code LongSummaryStatistics} can be used as a * {@linkplain java.util.stream.Stream#collect(Collector) reduction} * target for a {@linkplain java.util.stream.Stream stream}. For example: * * <pre> {@code * LongSummaryStatistics stats = people.stream() * .collect(Collectors.summarizingLong(Person::getAge)); *}</pre> * * This computes, in a single pass, the count of people, as well as the minimum, * maximum, sum, and average of their ages. * * @implNote This implementation is not thread safe. However, it is safe to use * {@link java.util.stream.Collectors#summarizingLong(java.util.function.ToLongFunction) * Collectors.summarizingLong()} on a parallel stream, because the parallel * implementation of {@link java.util.stream.Stream#collect Stream.collect()} * provides the necessary partitioning, isolation, and merging of results for * safe and efficient parallel execution. * * <p>This implementation does not check for overflow of the sum. * @since 1.8 */ public class LongSummaryStatistics implements LongConsumer, IntConsumer { private long count; private long sum; private long min = Long.MAX_VALUE; private long max = Long.MIN_VALUE; /** * Constructs an empty instance with zero count, zero sum, * {@code Long.MAX_VALUE} min, {@code Long.MIN_VALUE} max and zero * average. */ public LongSummaryStatistics() { } /** * Constructs a non-empty instance with the specified {@code count}, * {@code min}, {@code max}, and {@code sum}. * * <p>If {@code count} is zero then the remaining arguments are ignored and * an empty instance is constructed. * * <p>If the arguments are inconsistent then an {@code IllegalArgumentException} * is thrown. The necessary consistent argument conditions are: * <ul> * <li>{@code count >= 0}</li> * <li>{@code min <= max}</li> * </ul> * @apiNote * The enforcement of argument correctness means that the retrieved set of * recorded values obtained from a {@code LongSummaryStatistics} source * instance may not be a legal set of arguments for this constructor due to * arithmetic overflow of the source's recorded count of values. * The consistent argument conditions are not sufficient to prevent the * creation of an internally inconsistent instance. An example of such a * state would be an instance with: {@code count} = 2, {@code min} = 1, * {@code max} = 2, and {@code sum} = 0. * * @param count the count of values * @param min the minimum value * @param max the maximum value * @param sum the sum of all values * @throws IllegalArgumentException if the arguments are inconsistent * @since 10 */ public LongSummaryStatistics(long count, long min, long max, long sum) throws IllegalArgumentException { if (count < 0L) { throw new IllegalArgumentException("Negative count value"); } else if (count > 0L) { if (min > max) throw new IllegalArgumentException("Minimum greater than maximum"); this.count = count; this.sum = sum; this.min = min; this.max = max; } // Use default field values if count == 0 } /** * Records a new {@code int} value into the summary information. * * @param value the input value */ @Override public void accept(int value) { accept((long) value); } /** * Records a new {@code long} value into the summary information. * * @param value the input value */ @Override public void accept(long value) { ++count; sum += value; min = Math.min(min, value); max = Math.max(max, value); } /** * Combines the state of another {@code LongSummaryStatistics} into this * one. * * @param other another {@code LongSummaryStatistics} * @throws NullPointerException if {@code other} is null */ public void combine(LongSummaryStatistics other) { count += other.count; sum += other.sum; min = Math.min(min, other.min); max = Math.max(max, other.max); } /** * Returns the count of values recorded. * * @return the count of values */ public final long getCount() { return count; } /** * Returns the sum of values recorded, or zero if no values have been * recorded. * * @return the sum of values, or zero if none */ public final long getSum() { return sum; } /** * Returns the minimum value recorded, or {@code Long.MAX_VALUE} if no * values have been recorded. * * @return the minimum value, or {@code Long.MAX_VALUE} if none */ public final long getMin() { return min; } /** * Returns the maximum value recorded, or {@code Long.MIN_VALUE} if no * values have been recorded * * @return the maximum value, or {@code Long.MIN_VALUE} if none */ public final long getMax() { return max; } /** * Returns the arithmetic mean of values recorded, or zero if no values have been * recorded. * * @return The arithmetic mean of values, or zero if none */ public final double getAverage() { return getCount() > 0 ? (double) getSum() / getCount() : 0.0d; } /** * Returns a non-empty string representation of this object suitable for * debugging. The exact presentation format is unspecified and may vary * between implementations and versions. */ @Override public String toString() { return String.format("%s{count=%d, sum=%d, min=%d, average=%f, max=%d}", this.getClass().getSimpleName(), getCount(), getSum(), getMin(), getAverage(), getMax()); } }