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ToDoubleFunction Interface in Java with Examples
  • Last Updated : 08 Oct, 2018

The ToDoubleFunction Interface is a part of the java.util.function package which has been introduced since Java 8, to implement functional programming in Java. It represents a function which takes in an argument of type T and produces a double-valued result.

This functional interface takes in only one generic, namely:-

  • T: denotes the type of the input argument to the operation

The lambda expression assigned to an object of ToDoubleFunction type is used to define its applyAsDouble() which eventually applies the given operation on its only argument. It is similar to using an object of type Function<T, Double>.

The ToDoubleFunction interface has only one function:


This method accepts an argument of type T and gives a double-valued result.


double applyAsDouble(T value)

Parameters: This method takes in one parameter value which is an argument of type T.

Returns: This method returns a double-valued result.

Below is the code to illustrate applyAsDouble() method:


import java.util.function.ToDoubleFunction;
public class Main {
    public static void main(String args[])
        ToDoubleFunction<Integer> ob = a -> a / 2;
        // using applyAsDouble()

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