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ToLongFunction Interface in Java with Examples

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  • Last Updated : 08 Oct, 2018
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The ToLongFunction 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 long-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 ToLongFunction 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<T, Long>.

The ToLongFunction interface has only one function:


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


long applyAsLong(T value)

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

Returns: This method returns a long-valued result.

Below is the code to illustrate applyAsLong() method:


import java.util.function.ToLongFunction;
public class Main {
    public static void main(String args[])
        // Instantiating ToLongFunction
        ToLongFunction<Integer> ob = a -> a * 10000;
        // Applying the above function
        // using applyAsLong()


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