Java 8 New Features and Functional Programming Overview

This article provides a comprehensive overview of the major enhancements introduced in Java 8, focusing on functional programming constructs and modern APIs.

It explains lambda expressions, showing the concise syntax (parameters) -> expression and how they replace anonymous classes for cleaner code.

Functional interfaces are introduced, including built‑in types such as Consumer<T> , Supplier<T> , Function<T,R> , and Predicate<T> , with examples like @FunctionalInterface public interface MyFunc { T getValue(T t); } .

Method references are demonstrated as a shorthand for lambdas, e.g., List::size or Math::max , and constructor references such as ArrayList::new are shown.

The Stream API is covered in depth, illustrating creation ( Stream.of(...) , list.stream() ), intermediate operations (filter, map, flatMap, sorted), and terminal operations (forEach, collect, reduce). Sample code uses persons.stream().filter(p -> p.getAge() > 20).forEach(System.out::println); .

Parallel streams and their underlying Fork/Join framework are discussed, with guidance on when to use parallelism and how to configure the common pool.

New default and static methods in interfaces are highlighted, allowing backward‑compatible API evolution, exemplified by List.sort(Comparator.naturalOrder()) .

The Optional class is presented as a safer alternative to null , with usage patterns such as Optional.ofNullable(person).map(Person::getName).orElse("Unknown") .

CompletableFuture is introduced for composable asynchronous programming, showing creation and completion with CompletableFuture f = new CompletableFuture<>(); f.complete(100); and chaining operations.

Java 8’s new date‑time API is described, featuring immutable classes like LocalDate , LocalTime , LocalDateTime , and Instant , with formatting via DateTimeFormatter .

Additional language improvements are summarized, including enhanced atomic classes, ConcurrentHashMap bulk operations, new methods in Arrays , numeric utilities, and reflection enhancements for parameter names.