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Java compact1, compact2, compact3 java.util Class DoubleSummaryStatistics（JDK8）

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Java™ Platform
Standard Ed. 8
compact1, compact2, compact3
java.util

Class 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.

    • 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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Java™ Platform
Standard Ed. 8

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