java8.util

Class DoubleSummaryStatistics

java.lang.Object

java8.util.DoubleSummaryStatistics

All Implemented Interfaces:

DoubleConsumer

public class DoubleSummaryStatistics
extends java.lang.Object
implements DoubleConsumer

A state object for collecting statistics such as count, min, max, sum, and average.

This class is designed to work with (though does not require) streams. For example, you can compute summary statistics on a stream of doubles with:

 
 DoubleSummaryStatistics stats = doubleStream.collect(DoubleSummaryStatistics::new,
                                                      DoubleSummaryStatistics::accept,
                                                      DoubleSummaryStatistics::combine);
 

DoubleSummaryStatistics can be used as a reduction target for a stream. For example:

 
 DoubleSummaryStatistics stats = people.stream()
     .collect(Collectors.summarizingDouble(Person::getWeight));

This computes, in a single pass, the count of people, as well as the minimum, maximum, sum, and average of their weights.

Implementation Note:
This implementation is not thread safe. However, it is safe to use Collectors.toDoubleStatistics() on a parallel stream, because the parallel implementation of Stream.collect() provides the necessary partitioning, isolation, and merging of results for safe and efficient parallel execution.

Since:

1.8

Constructor Summary

Constructors

Constructor and Description
DoubleSummaryStatistics() Construct an empty instance with zero count, zero sum, Double.POSITIVE_INFINITY min, Double.NEGATIVE_INFINITY max and zero average.

Method Summary

Modifier and Type	Method and Description
void	accept(double value) Records another value into the summary information.
void	combine(DoubleSummaryStatistics other) Combines the state of another DoubleSummaryStatistics into this one.
double	getAverage() Returns the arithmetic mean of values recorded, or zero if no values have been recorded.
long	getCount() Return the count of values recorded.
double	getMax() Returns the maximum recorded value, Double.NaN if any recorded value was NaN or Double.NEGATIVE_INFINITY if no values were recorded.
double	getMin() Returns the minimum recorded value, Double.NaN if any recorded value was NaN or Double.POSITIVE_INFINITY if no values were recorded.
double	getSum() Returns the sum of values recorded, or zero if no values have been recorded.
java.lang.String	toString() Returns a non-empty string representation of this object suitable for debugging.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

DoubleSummaryStatistics

public DoubleSummaryStatistics()

Construct an empty instance with zero count, zero sum, Double.POSITIVE_INFINITY min, Double.NEGATIVE_INFINITY max and zero average.

Method Detail

accept

public void accept(double value)

Records another value into the summary information.

Specified by:

accept in interface DoubleConsumer

Parameters:

value - the input value

combine

public void combine(DoubleSummaryStatistics other)

Combines the state of another DoubleSummaryStatistics into this one.

Parameters:

other - another DoubleSummaryStatistics

Throws:

java.lang.NullPointerException - if other is null

getCount

public final long getCount()

Return the count of values recorded.

Returns:

the count of values

getSum

public final double getSum()

Returns the sum of values recorded, or zero if no values have been recorded. If any recorded value is a NaN or the sum is at any point a NaN then the sum will be NaN.

The value of a floating-point sum is a function both of the input values as well as the order of addition operations. The order of addition operations of this method is intentionally not defined to allow for implementation flexibility to improve the speed and accuracy of the computed result. In particular, this method may be implemented using compensated summation or other technique to reduce the error bound in the numerical sum compared to a simple summation of double values.

API Note:
Values sorted by increasing absolute magnitude tend to yield more accurate results.

Returns:

the sum of values, or zero if none

getMin

public final double getMin()

Returns the minimum recorded value, Double.NaN if any recorded value was NaN or 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.

Returns:

the minimum recorded value, Double.NaN if any recorded value was NaN or Double.POSITIVE_INFINITY if no values were recorded

getMax

public final double getMax()

Returns the maximum recorded value, Double.NaN if any recorded value was NaN or 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.

Returns:

the maximum recorded value, Double.NaN if any recorded value was NaN or Double.NEGATIVE_INFINITY if no values were recorded

getAverage

public final double getAverage()

Returns the arithmetic mean of values recorded, or zero if no values have been recorded. If any recorded value is a NaN or the sum is at any point a NaN then the average will be code NaN.

The average returned can vary depending upon the order in which values are recorded. This method may be implemented using compensated summation or other technique to reduce the error bound in the numerical sum used to compute the average.

API Note:
Values sorted by increasing absolute magnitude tend to yield more accurate results.

Returns:

the arithmetic mean of values, or zero if none

toString

public java.lang.String toString()

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.

Overrides:

toString in class java.lang.Object