Thinking|functional programming - define Java|in

Although Java is not a functional language, Java 8 Lamda Expressions and Method References allow we to program in a functional style.
We can think OO abstracts data, FP abstracts behavior.
In computer science, functional programming is a programming paradigm. It set once and never changed.
【Thinking|functional programming - define】for example:

// functional/Strategize.java // (c)2017 MindView LLC: see Copyright.txt // We make no guarantees that this code is fit for any purpose. // Visit http://OnJava8.com for more book information.interface Strategy { String approach(String msg); }class Soft implements Strategy { public String approach(String msg) { return msg.toLowerCase() + "?"; } }class Unrelated { static String twice(String msg) { return msg + " " + msg; } }public class Strategize { Strategy strategy; String msg; Strategize(String msg) { strategy = new Soft(); // [1] this.msg = msg; }void communicate() { System.out.println(strategy.approach(msg)); }void changeStrategy(Strategy strategy) { this.strategy = strategy; }public static void main(String[] args) { Strategy[] strategies = { new Strategy() { // [2] public String approach(String msg) { return msg.toUpperCase() + "!"; } }, msg -> msg.substring(0, 5), // [3] // lambda expression Unrelated::twice // [4] // Java 8 method reference }; Strategize s = new Strategize("Hello there"); s.communicate(); for (Strategy newStrategy : strategies) { s.changeStrategy(newStrategy); // [5] s.communicate(); // [6] } } } /* Output: hello there? HELLO THERE! Hello Hello there Hello there */

references:
1. On Java 8 - Bruce Eckel
2. https://en.wikipedia.org/wiki/Functional_programming#Concepts
3. https://github.com/wangbingfeng/OnJava8-Examples/blob/master/functional/Strategize.java