DoubleFunction Interface in Java with Examples

The DoubleFunction 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 a double-valued argument and produces a result of type R.

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

• R: denotes the type of the output of this function

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

The DoubleFunction interface has only one function:

apply()

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

Syntax:

R apply(double value)

Parameters: This method takes in one parameter value which is a double-valued argument.

Returns: This method returns a value of type R.

Below is the code to illustrate apply() method:

Program

import java.util.function.DoubleFunction;

public class Main {
    public static void main(String args[])
    {
        DoubleFunction<Integer> ob = a -> (int)(a * 10);

        // Using apply() method
        System.out.println(ob.apply(3.2));
    }
}

Output:

32