# Uses of Interface
java.util.function.ToDoubleFunction

Packages that use ToDoubleFunction
Package
Description
java.util
Contains the collections framework, some internationalization support classes, a service loader, properties, random number generation, string parsing and scanning classes, base64 encoding and decoding, a bit array, and several miscellaneous utility classes.
java.util.concurrent
Utility classes commonly useful in concurrent programming.
java.util.stream
Classes to support functional-style operations on streams of elements, such as map-reduce transformations on collections.

- ## Uses of ToDoubleFunction in java.util

  Methods in java.util with parameters of type ToDoubleFunction
  Modifier and Type
  Method
  Description
  `static <T> Comparator<T>`
  Comparator.`comparingDouble(ToDoubleFunction<? super T> keyExtractor)`
  Accepts a function that extracts a `double` sort key from a type `T`, and returns a `Comparator<T>` that compares by that sort key.
  `default Comparator<T>`
  Comparator.`thenComparingDouble(ToDoubleFunction<? super T> keyExtractor)`
  Returns a lexicographic-order comparator with a function that extracts a `double` sort key.

- ## Uses of ToDoubleFunction in java.util.concurrent

  Methods in java.util.concurrent with parameters of type ToDoubleFunction
  Modifier and Type
  Method
  Description
  `double`
  ConcurrentHashMap.`reduceEntriesToDouble(long parallelismThreshold, ToDoubleFunction<Map.Entry<K,V>> transformer, double basis, DoubleBinaryOperator reducer)`
  Returns the result of accumulating the given transformation of all entries using the given reducer to combine values, and the given basis as an identity value.
  `double`
  ConcurrentHashMap.`reduceKeysToDouble(long parallelismThreshold, ToDoubleFunction<? super K> transformer, double basis, DoubleBinaryOperator reducer)`
  Returns the result of accumulating the given transformation of all keys using the given reducer to combine values, and the given basis as an identity value.
  `double`
  ConcurrentHashMap.`reduceValuesToDouble(long parallelismThreshold, ToDoubleFunction<? super V> transformer, double basis, DoubleBinaryOperator reducer)`
  Returns the result of accumulating the given transformation of all values using the given reducer to combine values, and the given basis as an identity value.

- ## Uses of ToDoubleFunction in java.util.stream

  Methods in java.util.stream with parameters of type ToDoubleFunction
  Modifier and Type
  Method
  Description
  `static <T> Collector<T,?,Double>`
  Collectors.`averagingDouble(ToDoubleFunction<? super T> mapper)`
  Returns a `Collector` that produces the arithmetic mean of a double-valued function applied to the input elements.
  `DoubleStream`
  Stream.`mapToDouble(ToDoubleFunction<? super T> mapper)`
  Returns a `DoubleStream` consisting of the results of applying the given function to the elements of this stream.
  `static <T> Collector<T, ?, DoubleSummaryStatistics>`
  Collectors.`summarizingDouble(ToDoubleFunction<? super T> mapper)`
  Returns a `Collector` which applies an `double`-producing mapping function to each input element, and returns summary statistics for the resulting values.
  `static <T> Collector<T,?,Double>`
  Collectors.`summingDouble(ToDoubleFunction<? super T> mapper)`
  Returns a `Collector` that produces the sum of a double-valued function applied to the input elements.