DoubleSummaryStatistics (Java Platform SE 8 )
Keywords: java.util.DoubleSummaryStatistics class
Date: 2015-05-24

compact1, compact2, compact3
java.util

## Class DoubleSummaryStatistics

- java.lang.Object
- - java.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.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

    All Methods Instance Methods Concrete Methods
    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 string representation of the object.

    - ### Methods inherited from class java.lang.Object

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

    - ### Methods inherited from interface java.util.function.DoubleConsumer

      `andThen`

- - ### 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:
        `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 String toString()

      Returns a string representation of the object. In general, the `toString` method returns a string that "textually represents" this object. The result should be a concise but informative representation that is easy for a person to read. It is recommended that all subclasses override this method.

      The `toString` method for class `Object` returns a string consisting of the name of the class of which the object is an instance, the at-sign character ``@`', and the unsigned hexadecimal representation of the hash code of the object. In other words, this method returns a string equal to the value of:

      >      getClass().getName() + '@' + Integer.toHexString(hashCode())

      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 the object.

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