97 Things Every Java Programmer Should Know

Chapter 44. The JVM Is a Multiparadigm Platform: Use This to Improve Your Programming

Russel Winder

Java is an imperative language: Java programs tell the JVM what to do and when to do it. But computing is all about building abstractions. Java is touted as an object-oriented language: the abstractions of Java are objects, methods, and message passing via method call. Over the years, people have built larger and larger systems using objects, methods, updatable state, and explicit iteration, and the cracks have appeared. Many are “papered over” using high quality testing, but still programmers end up “hacking” to get around various problems.

With the arrival of Java 8, Java underwent an extremely revolutionary change: it introduced method references, lambda expressions, default methods on interfaces, higher order functions, implicit iteration, and various other things. Java 8 introduced a very different way of thinking about the implementation of algorithms.

Imperative and declarative thinking are very different ways of expressing algorithms. During the 1980s and 1990s, these mindsets were seen as being distinct and irreconcilable: we had the object-oriented versus functional programming war. Smalltalk and C++ were the champions of object-orientation, and Haskell was the champion of functional. Later, C++ stopped being an object-oriented language and marketed itself as a multiparadigm ...