---
title: "What are functional interfaces used for in Java 8?"  
description: "What are functional interfaces used for in Java 8?"  
author: "Sandra Emily"  
published: 2023-08-17  
updated: 2023-08-18  
canonical: https://www.mindstick.com/forum/159556/what-are-functional-interfaces-used-for-in-java-8  
category: "java"  
tags: ["java", "interface", "functions"]  
reading_time: 2 minutes  

---

# What are functional interfaces used for in Java 8?

What are [functional](https://www.mindstick.com/articles/13005/the-functional-aspects-of-laser-technology) [interfaces](https://www.mindstick.com/articles/12100/interfaces-in-java-real-life-example) used for in [Java](https://www.mindstick.com/articles/12214/web-development-company-in-india-laid-on-the-foundation-of-concrete-java-programming) 8?

## Replies

### Reply by Aryan Kumar

Functional interfaces are used in Java 8 for a variety of purposes, including:

- **Declaring anonymous functions:** Functional interfaces can be used to declare anonymous functions, which are functions that are not defined in a separate named method. Anonymous functions can be used in a variety of places, such as in lambda expressions and method references.
- **Implementing interfaces with a single abstract method:** Functional interfaces can be used to implement interfaces with a single abstract method. This makes it easier to implement interfaces and to write code that is more modular and reusable.
- **Passing functions as arguments:** Functional interfaces can be passed as arguments to methods. This allows you to pass a function to a method without having to create a separate object to represent the function.
- **Referencing methods:** Functional interfaces can be used to reference methods. This allows you to use a method as if it were a function.

Here are some examples of how functional interfaces are used in Java 8:

- The `Runnable` interface is a functional interface that declares a single abstract method, `run()`. The `run()` method is executed when the `Runnable` object is executed.
- The `Comparator` interface is a functional interface that declares two abstract methods, `compare()` and `equals()`. The `compare()` method compares two objects and returns an integer indicating their relative order. The `equals()` method compares two objects and returns a boolean value indicating whether the objects are equal.
- The `Predicate` interface is a functional interface that declares a single abstract method, `test()`. The `test()` method takes an object as its input and returns a boolean value indicating whether the object satisfies the predicate.


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