Functional Programming in Java 8: Tips and Tricks

By NIIT Editorial

Published on 06/07/2023

Functional programming is a paradigm of computer programming that places an emphasis on the usage of pure functions that do not have any side effects and work on data that is not possible to be changed. Java 8 brought new capabilities for functional programming, which make it possible for developers to construct code that is both more succinct and more expressive. 

This article will discuss the significance of functional programming in Java 8 and provide advice on how to make the most of the language's capabilities.


Table of Contents:

  • Functional Interfaces 
  • Lambda Expressions 
  • Stream API 
  • Method Reference 
  • Optional Class 
  • Parallel Streams 
  • Conclusion


Functional Programming in Java 8

In functional programming, the focus is on writing code in the form of "pure functions." A pure function is one that acts just on its inputs and does not produce any outputs. The output is independent of any conditions other than those specified by the inputs. This makes it simpler to understand the function's behaviour and reduces the likelihood of making mistakes.

Developers may now take use of new functional programming techniques introduced in Java 8 to create code that is both shorter and more evocative. Lambda expressions, functional interfaces, the Stream API, the Reference to Methods, and the Optional class are all examples of such features.


1. Importance of Functional Programming in Java 8

The functional programming enhancements introduced in Java 8 facilitate the creation of code that is both compact and evocative. As a result, developers may create code that is less complicated to update, simpler to understand, and less prone to mistakes.


2. Tips and Tricks

  • Use lambda expressions to create clear and concise programmes.
  • To specify the signature of lambda expressions, use functional interfaces.
  • Transform data sets using the Stream API
  • To make lambda expressions easier to understand, use the reference approach.
  • When dealing with null values, use the Optional class.
  • If you're using a multi-core machine, you should take use of parallel streams.


Functional Interfaces

Functional interfaces are interfaces that have only one abstract method. They are used to define the signature of lambda expressions.


1. Understanding the Syntax of Functional Interfaces

The syntax for defining a functional interface is as follows:




public interface MyFunctionalInterface {

    public void myMethod();



2. Built-in Functional Interfaces

Java 8 provides several built-in functional interfaces that can be used as the signature of lambda expressions. These include Predicate, Function, Consumer, and Supplier.


3. Example of Creating Custom Functional Interfaces

Here's an example of creating a custom functional interface:



public interface MyFunctionalInterface {

    public void myMethod(String s);



Lambda Expressions

Lambda expressions are anonymous functions that can be passed around like values and used as the implementation of functional interfaces.

The syntax for a lambda expression is as follows:


(parameters) -> expression


1. Types of Lambda Expressions

There are two types of lambda expressions in Java: expression lambdas and statement lambdas.


2. Advantages of Using Lambda Expressions

Lambda expressions make it easier to write more concise and expressive code. They allow developers to pass behaviour around as if it were data.


3. Examples of Using Lambda Expressions

Here's an example of using a lambda expression:


List names = Arrays.asList("John", "Jane", "Joe");

names.forEach(name -> System.out.println(name));


Stream API

The Stream API is a new API in Java 8 that provides a way to process collections of data using functional programming techniques.

The syntax for the Stream API is as follows:


Stream stream =;


1. Understanding the Intermediate and Terminal Operations in Stream API

The Stream API provides intermediate and terminal operations. Intermediate operations return a new stream that can be further processed, while terminal operations return a result or a side effect. Examples of intermediate operations include filter, map, and flatMap, while examples of terminal operations include forEach, collect, and reduce.


2. Examples of Using Stream API

Here's an example of using the Stream API to filter and print out names that start with "J":



List names = Arrays.asList("John", "Jane", "Joe");

     .filter(name -> name.startsWith("J"))



Method Reference

Method reference is a shorthand syntax for lambda expressions that allows developers to refer to an existing method and use it as the implementation of a functional interface.

The syntax for method reference is as follows:




1. Types of Method Reference

There are four types of method reference in Java: static method reference, instance method reference, constructor reference, and array constructor reference.


2. Advantages of Using Method Reference

Method reference allows developers to write more concise and expressive code. It simplifies lambda expressions and makes the code easier to read and write.


3. Examples of using Method Reference

Here's an example of using method reference:


List names = Arrays.asList("John", "Jane", "Joe");



Optional Class

The Optional class is a container object that may or may not contain a non-null value.

The syntax for using the Optional class is as follows:


Optional optionalName = Optional.ofNullable(name);

if (optionalName.isPresent()) {

    String upperCaseName = optionalName.get().toUpperCase();



1. Understanding the Advantages of Optional Class

The Optional class helps developers handle null values more elegantly. It forces developers to consider the possibility of null values and provides a more expressive way of dealing with them.


2. Examples of using Optional Class

Here's an example of using the Optional class to handle null values:


String name = null;

Optional optionalName = Optional.ofNullable(name);

String upperCaseName ="Unknown");


Parallel Streams

Parallel streams are a way to process collections of data in parallel using multiple threads.

The syntax for using parallel streams is the same as for regular streams, but with the addition of the parallel() method.


List names = Arrays.asList("John", "Jane", "Joe");



1. Advantages of using Parallel Streams

Parallel streams can improve performance on multi-core processors, allowing for faster processing of large data sets.


2. Examples of Using Parallel Streams

Here's an example of using parallel streams to process a large data set:


List numbers = IntStream.range(0, 10000000)



int sum = numbers.parallelStream().mapToInt(Integer::intValue).sum();



Developers are able to create code that is both more succinct and expressive thanks to the functional programming techniques introduced in Java 8. For example, you can use lambda expressions to write code that is concise and expressive; you can use functional interfaces to define the signature of lambda expressions; you can use the Stream API to process collections of data; you can use method reference to simplify lambda expressions; you can use the Optional class to handle null values; and you can use parallel streams to improve performance on multi-core processors. These are just some of the tips and tricks you can use to get the most out of these features.

Because Java 8 provides support for functional programming features, it is now much simpler for software developers to embrace the functional programming paradigm, which is becoming an increasingly prominent programming paradigm in the world of software development. When developers use functional programming, they are able to design code that is both more succinct and more expressive. This, in turn, improves the readability, maintainability, and scalability of their codebase.

The introduction of functional programming tools in Java 8 is merely the beginning of an ongoing trend in Java towards greater functional programming. We should anticipate more support for functional programming capabilities in future editions of the Java programming language as the language continues to undergo evolution.

As a conclusion, the support for functional programming that was included in Java 8 has given developers access to new opportunities to construct code that is both more expressive and more succinct. Developers are able to design code that is easier to maintain and scale when they use functional programming features such as lambda expressions, functional interfaces, the Stream API, method reference, the Optional class, and parallel streams. In the world of software development, functional programming is continuing to gather steam, and as a result, we may anticipate seeing even greater support for this programming paradigm in next iterations of the Java programming language. It is crucial to stay up with current developments and continue to enhance your abilities in functional programming if you are a Java developer, and a Java developer course will help you reach those goals. If you are interested in learning more about Java development, visit our website.