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: + *
{@code
+ * LongSummaryStatistics stats = longStream.collect(LongSummaryStatistics::new,
+ * LongSummaryStatistics::accept,
+ * LongSummaryStatistics::combine);
+ * }
+ *
+ * {@code LongSummaryStatistics} can be used as a + * {@linkplain java.util.stream.Stream#reduce(java.util.function.BinaryOperator) reduction} + * target for a {@linkplain java.util.stream.Stream stream}. For example: + * + *
{@code
+ * LongSummaryStatistics stats = people.stream()
+ * .collect(Collectors.toLongSummaryStatistics(Person::getAge));
+ *}
+ *
+ * This computes, in a single pass, the count of people, as well as the minimum,
+ * maximum, sum, and average of their ages in milliseconds.
+ *
+ * @implNote This implementation is not thread safe. However, it is safe to use
+ * {@link java.util.stream.Collectors#toLongSummaryStatistics(java.util.function.ToLongFunction)
+ * Collectors.toLongStatistics()} 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.
+ *
+ * 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; + + /** + * Construct an empty instance with zero count, zero sum, + * {@code Long.MAX_VALUE} min, {@code Long.MIN_VALUE} max and zero + * average. + */ + public LongSummaryStatistics() { } + + /** + * 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 average of values recorded, or zero if no values have been + * recorded. + * + * @return The average of values, or zero if none + */ + public final double getAverage() { + return getCount() > 0 ? (double) getSum() / getCount() : 0.0d; + } + + @Override + /** + * {@inheritDoc} + * + * 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. + */ + public String toString() { + return String.format( + "%s{count=%d, sum=%d, min=%d, average=%d, max=%d}", + this.getClass().getSimpleName(), + getCount(), + getSum(), + getMin(), + getAverage(), + getMax()); + } +}