java8.util

Class DoubleSummaryStatistics

java.lang.Object

java8.util.DoubleSummaryStatistics

All Implemented Interfaces:

DoubleConsumer

public class DoubleSummaryStatistics
extends 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.summarizingDouble() 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() Constructs an empty instance with zero count, zero sum, Double.POSITIVE_INFINITY min, Double.NEGATIVE_INFINITY max and zero average.
DoubleSummaryStatistics(long count, double min, double max, double sum) Constructs a non-empty instance with the specified count, min, max, and sum.

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.
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()

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

DoubleSummaryStatistics

public DoubleSummaryStatistics(long count,
                               double min,
                               double max,
                               double sum)
                        throws IllegalArgumentException

Constructs a non-empty instance with the specified count, min, max, and sum.

If count is zero then the remaining arguments are ignored and an empty instance is constructed.

If the arguments are inconsistent then an IllegalArgumentException is thrown. The necessary consistent argument conditions are:

• count >= 0
• (min <= max && !isNaN(sum)) || (isNaN(min) && isNaN(max) && isNaN(sum))

API Note:
The enforcement of argument correctness means that the retrieved set of recorded values obtained from a DoubleSummaryStatistics 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: count = 2, min = 1, max = 2, and sum = 0.

Parameters:

count - the count of values

min - the minimum value

max - the maximum value

sum - the sum of all values

Throws:

IllegalArgumentException - if the arguments are inconsistent

Since:

10

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:

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.

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. Because of the unspecified order of operations and the possibility of using differing summation schemes, the output of this method may vary on the same input values.

Various conditions can result in a non-finite sum being computed. This can occur even if the all the recorded values being summed are finite. If any recorded value is non-finite, the sum will be non-finite:

• If any recorded value is a NaN, then the final sum will be NaN.
• If the recorded values contain one or more infinities, the sum will be infinite or NaN.
  • If the recorded values contain infinities of opposite sign, the sum will be NaN.
  • If the recorded values contain infinities of one sign and an intermediate sum overflows to an infinity of the opposite sign, the sum may be NaN.

It is possible for intermediate sums of finite values to overflow into opposite-signed infinities; if that occurs, the final sum will be NaN even if the recorded values are all finite. If all the recorded values are zero, the sign of zero is not guaranteed to be preserved in the final sum.

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.

The computed average can vary numerically and have the special case behavior as computing the sum; see getSum() for details.

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 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 Object

Returns:

a string representation of this object