Java 8 | DoubleToLongFunction Interface in Java with Examples

The DoubleToLongFunction 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 gives an long-valued result.

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

The DoubleToLongFunction interface has only one function:

1. applyAsLong() : This method accepts a double-valued argument and gives an long-valued result.


long applyAsLong(double value)

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

Returns: This method returns an long-valued result.

Below is the code to illustrate applyAsLong() method:






// Java Program to demonstrate
// DoubleToLongFunction's applyAsLong() method
import java.util.function.DoubleToLongFunction;
public class Main {
    public static void main(String args[])
        // Declare the DoubleToLongFunction
        DoubleToLongFunction truncate = a -> (long)a;
        // Apply the function to get the result as long
        // using applyAsLong()




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