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Introduction to Java 8

Released in March 2014, Java 8 is widely considered the most revolutionary and significant release in the history of the Java programming language.

Before Java 8, Java was a strictly, purely Object-Oriented language. Everything had to be an object, and every piece of logic had to live inside a method inside a class. Java 8 changed everything by introducing Functional Programming paradigms into the language.

Why was Java 8 so revolutionary?​

The primary motivation behind Java 8 was to enable developers to write cleaner, more concise code and to take full advantage of multi-core processors.

To achieve this, the Java architects introduced a suite of highly interconnected features:

  1. Functional Interfaces: The foundation that allows methods to be treated as variables.
  2. Lambda Expressions: The syntax that allows you to write anonymous, inline functions without the heavy boilerplate of classes.
  3. The Stream API: A powerful new way to process collections of objects in a functional, declarative manner (and easily process them in parallel).
  4. The Optional Class: A complete paradigm shift in how developers handle null values to avoid the dreaded NullPointerException.
  5. Default Methods: A mechanism that allowed interfaces to have implemented methods, ensuring massive additions (like Streams) wouldn't break older, legacy codebases.
  6. The New Date/Time API: A complete overhaul of the broken, legacy java.util.Date class, introducing modern, immutable classes like LocalDate and LocalDateTime.

The Learning Curve​

Because these features are deeply interconnected, they must be learned in a specific order.

You cannot truly understand Lambdas without first understanding Functional Interfaces. You cannot effectively use the Stream API without knowing how to write Lambdas. And you cannot process the results of a Stream without understanding Optionals.

In the following modules, we will walk through each of these revolutionary features step-by-step. Let's begin with the foundation: Functional Interfaces.