dtonhofer

dtonhofer

Functional Programming in Java, Second Edition: Code for "Chapter 7, Lazy Evaluations" in one file

Nothing special:

package chapter7;

import org.junit.jupiter.api.Test;

import java.util.List;
import java.util.function.Supplier;
import java.util.stream.Stream;

public class BeingLazy_LazyEvaluations {

    private final static List<String> names = List.of("Brad", "Kate", "Kim", "Jack", "Joe", "Mike", "Susan", "George", "Robert", "Julia", "Parker", "Benson");
    
    // "lazy/fpij/Evaluation.java" on p. 127, p.128

    private static boolean evaluate(final int value) {
        System.out.println("evaluating ..." + value);
        simulateTimeConsumingOp(2000);
        return value > 100;
    }

    private static void simulateTimeConsumingOp(long time_ms) {
        try {
            Thread.sleep(time_ms);
        } catch (InterruptedException ex) {
            throw new RuntimeException(ex);
        }
    }

    // "lazy/fpij/Evaluation.java" p. 127

    private static void eagerEvaluator(final boolean input1, final boolean input2) {
        System.out.println("eagerEvaluator called...");
        System.out.println("accept?: " + (input1 && input2));
    }

    // "lazy/fpij/Evaluation.java" p. 128

    private static void lazyEvaluator(final Supplier<Boolean> input1, final Supplier<Boolean> input2) {
        System.out.println("lazyEvaluator called...");
        System.out.println("accept?: " + (input1.get() && input2.get()));
    }

    // "lazy/fpij/LazyStreams.java" on p.130

    private static int length(final String name) {
        System.out.println("getting length for " + name);
        return name.length();
    }

    // "lazy/fpij/LazyStreams.java" on p.130

    private static String toUpper(final String name) {
        System.out.println("converting to uppercase: " + name);
        return name.toUpperCase();
    }

    // "lazy/fpij/Evaluation.java" on p.127

    @Test
    void evaluateEagerly() {
        eagerEvaluator(evaluate(1), evaluate(2));
    }

    // "lazy/fpij/Evaluation.java" on p.128

    @Test
    void evaluateLazily() {
        lazyEvaluator(() -> evaluate(1), () -> evaluate(2));
    }

    // "lazy/fpij/LazyStreams.java" on p.130
    // ".map(name -> toUpper(name))" replaced with ".map(LazyStreams::toUpper)"

    @Test
    void lazyStream() {
        final String firstNameWith3Letters =
                names.stream()
                        .filter(name -> length(name) == 3)
                        .map(BeingLazy_LazyEvaluations::toUpper)
                        .findFirst()
                        .orElse("");
        System.out.println(firstNameWith3Letters);
    }

    // lazy/fpij/LazyStreams.java on p.132
    // ".map(name -> toUpper(name))" replaced with ".map(LazyStreams::toUpper)"

    @Test
    void peekingIntoLaziness() {
        Stream<String> namesWith3Letters =
                names.stream()
                        .filter(name -> length(name) == 3)
                        .map(BeingLazy_LazyEvaluations::toUpper);
        System.out.println("Stream created, filtered, mapped...");
        System.out.println("ready to call findFirst...");
        final String firstNameWith3Letters =
                namesWith3Letters
                        .findFirst()
                        .orElse("");
        System.out.println(firstNameWith3Letters);
    }

}

Where Next?

Popular Pragmatic Bookshelf topics Top

jon
Some minor things in the paper edition that says “3 2020” on the title page verso, not mentioned in the book’s errata online: p. 186 But...
New
joepstender
The generated iex result below should list products instead of product for the metadata. (page 67) iex&gt; product = %Product{} %Pento....
New
patoncrispy
I’m new to Rust and am using this book to learn more as well as to feed my interest in game dev. I’ve just finished the flappy dragon exa...
New
AndyDavis3416
@noelrappin Running the webpack dev server, I receive the following warning: ERROR in tsconfig.json TS18003: No inputs were found in c...
New
jskubick
I’m running Android Studio “Arctic Fox” 2020.3.1 Patch 2, and I’m embarrassed to admit that I only made it to page 8 before running into ...
New
brunogirin
When installing Cards as an editable package, I get the following error: ERROR: File “setup.py” not found. Directory cannot be installe...
New
rainforest
Hi, I’ve got a question about the implementation of PubSub when using a Phoenix.Socket.Transport behaviour rather than channels. Before ...
New
bjnord
Hello @herbert ! Trying to get the very first “Hello, Bracket Terminal!" example to run (p. 53). I develop on an Amazon EC2 instance runn...
New
dachristenson
@mfazio23 Android Studio will not accept anything I do when trying to use the Transformations class, as described on pp. 140-141. Googl...
New
New

Other popular topics Top

PragmaticBookshelf
Instantly view the changes you make to an app with stateful hot reload, and define a declarative UI in the same language as the app logic...
New
PragmaticBookshelf
Stop developing web apps with yesterday’s tools. Today, developers are increasingly adopting Clojure as a web-development platform. See f...
New
PragmaticBookshelf
Learn from the award-winning programming series that inspired the Elixir language, and go on a step-by-step journey through the most impo...
New
PragmaticBookshelf
Ruby, Io, Prolog, Scala, Erlang, Clojure, Haskell. With Seven Languages in Seven Weeks, by Bruce A. Tate, you’ll go beyond the syntax—and...
New
PragmaticBookshelf
Write Elixir tests that you can be proud of. Dive into Elixir’s test philosophy and gain mastery over the terminology and concepts that u...
New
AstonJ
You might be thinking we should just ask who’s not using VSCode :joy: however there are some new additions in the space that might give V...
New
AstonJ
This looks like a stunning keycap set :orange_heart: A LEGENDARY KEYBOARD LIVES ON When you bought an Apple Macintosh computer in the e...
New
CommunityNews
A Brief Review of the Minisforum V3 AMD Tablet. Update: I have created an awesome-minisforum-v3 GitHub repository to list information fo...
New
AnfaengerAlex
Hello, I’m a beginner in Android development and I’m facing an issue with my project setup. In my build.gradle.kts file, I have the foll...
New
mindriot
Ok, well here are some thoughts and opinions on some of the ergonomic keyboards I have, I guess like mini review of each that I use enoug...
New

Latest in Functional Programming in Java, Second Edition

Functional Programming in Java, Second Edition Portal ❯

Sub Categories: