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 doubles with: *
{@code
* DoubleSummaryStatistics stats = doubleStream.collect(DoubleSummaryStatistics::new,
* DoubleSummaryStatistics::accept,
* DoubleSummaryStatistics::combine);
* }
*
* {@code DoubleSummaryStatistics} 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
* DoubleSummaryStatistics stats = people.stream()
* .collect(Collectors.toDoubleSummaryStatistics(Person::getWeight));
*}
*
* This computes, in a single pass, the count of people, as well as the minimum,
* maximum, sum, and average of their weights.
*
* @implNote This implementation is not thread safe. However, it is safe to use
* {@link java.util.stream.Collectors#toDoubleSummaryStatistics(java.util.function.ToDoubleFunction)
* Collectors.toDoubleStatistics()} 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.
* @since 1.8
*/
public class DoubleSummaryStatistics implements DoubleConsumer {
private long count;
private double sum;
private double min = Double.POSITIVE_INFINITY;
private double max = Double.NEGATIVE_INFINITY;
/**
* Construct an empty instance with zero count, zero sum,
* {@code Double.POSITIVE_INFINITY} min, {@code Double.NEGATIVE_INFINITY}
* max and zero average.
*/
public DoubleSummaryStatistics() { }
/**
* Records another value into the summary information.
*
* @param value the input value
*/
@Override
public void accept(double value) {
++count;
sum += value;
min = Math.min(min, value);
max = Math.max(max, value);
}
/**
* Combines the state of another {@code DoubleSummaryStatistics} into this
* one.
*
* @param other another {@code DoubleSummaryStatistics}
* @throws NullPointerException if {@code other} is null
*/
public void combine(DoubleSummaryStatistics other) {
count += other.count;
sum += other.sum;
min = Math.min(min, other.min);
max = Math.max(max, other.max);
}
/**
* Return 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. The sum returned can vary depending upon the order in which
* values are recorded. This is due to accumulated rounding error in
* addition of values of differing magnitudes. Values sorted by increasing
* absolute magnitude tend to yield more accurate results. If any recorded
* value is a {@code NaN} or the sum is at any point a {@code NaN} then the
* sum will be {@code NaN}.
*
* @return the sum of values, or zero if none
*/
public final double getSum() {
return sum;
}
/**
* Returns the minimum recorded value, {@code Double.NaN} if any recorded
* value was NaN or {@code Double.POSITIVE_INFINITY} if no values were
* recorded. Unlike the numerical comparison operators, this method
* considers negative zero to be strictly smaller than positive zero.
*
* @return the minimum recorded value, {@code Double.NaN} if any recorded
* value was NaN or {@code Double.POSITIVE_INFINITY} if no values were
* recorded
*/
public final double getMin() {
return min;
}
/**
* Returns the maximum recorded value, {@code Double.NaN} if any recorded
* value was NaN or {@code Double.NEGATIVE_INFINITY} if no values were
* recorded. Unlike the numerical comparison operators, this method
* considers negative zero to be strictly smaller than positive zero.
*
* @return the maximum recorded value, {@code Double.NaN} if any recorded
* value was NaN or {@code Double.NEGATIVE_INFINITY} if no values were
* recorded
*/
public final double getMax() {
return max;
}
/**
* Returns the average of values recorded, or zero if no values have been
* recorded. The average returned can vary depending upon the order in
* which values are recorded. This is due to accumulated rounding error in
* addition of values of differing magnitudes. Values sorted by increasing
* absolute magnitude tend to yield more accurate results. If any recorded
* value is a {@code NaN} or the sum is at any point a {@code NaN} then the
* average will be {@code NaN}.
*
* @return the average of values, or zero if none
*/
public final double getAverage() {
return getCount() > 0 ? getSum() / getCount() : 0.0d;
}
/**
* {@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.
*/
@Override
public String toString() {
return String.format(
"%s{count=%d, sum=%f, min=%f, average=%f, max=%f}",
this.getClass().getSimpleName(),
getCount(),
getSum(),
getMin(),
getAverage(),
getMax());
}
}