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

brianokken
Many tasks_proj/tests directories exist in chapters 2, 3, 5 that have tests that use the custom markers smoke and get, which are not decl...
New
jeffmcompsci
Title: Design and Build Great Web APIs - typo “https://company-atk.herokuapp.com/2258ie4t68jv” (page 19, third bullet in URL list) Typo:...
New
ianwillie
Hello Brian, I have some problems with running the code in your book. I like the style of the book very much and I have learnt a lot as...
New
jdufour
Hello! On page xix of the preface, it says there is a community forum "… for help if your’re stuck on one of the exercises in this book… ...
New
Mmm
Hi, build fails on: bracket-lib = “~0.8.1” when running on Mac Mini M1 Rust version 1.5.0: Compiling winit v0.22.2 error[E0308]: mi...
New
raul
Page 28: It implements io.ReaderAt on the store type. Sorry if it’s a dumb question but was the io.ReaderAt supposed to be io.ReadAt? ...
New
Charles
In general, the book isn’t yet updated for Phoenix version 1.6. On page 18 of the book, the authors indicate that an auto generated of ro...
New
taguniversalmachine
It seems the second code snippet is missing the code to set the current_user: current_user: Accounts.get_user_by_session_token(session["...
New
dtonhofer
@parrt In the context of Chapter 4.3, the grammar Java.g4, meant to parse Java 6 compilation units, no longer passes ANTLR (currently 4....
New
New

Other popular topics Top

AstonJ
I’ve been hearing quite a lot of comments relating to the sound of a keyboard, with one of the most desirable of these called ‘thock’, he...
New
New
AstonJ
I ended up cancelling my Moonlander order as I think it’s just going to be a bit too bulky for me. I think the Planck and the Preonic (o...
New
AstonJ
If you want a quick and easy way to block any website on your Mac using Little Snitch simply… File &gt; New Rule: And select Deny, O...
New
New
PragmaticBookshelf
Develop, deploy, and debug BEAM applications using BEAMOps: a new paradigm that focuses on scalability, fault tolerance, and owning each ...
New
sir.laksmana_wenk
I’m able to do the “artistic” part of game-development; character designing/modeling, music, environment modeling, etc. However, I don’t...
New
PragmaticBookshelf
A masterclass in the fundamentals and principles of functional programming. Minh Quang Tran The Art of Functional Programming is a ma...
New
pragdave
Build robust LLM-powered apps, chatbots, and agents while mastering AI engineering principles that will help you outlast the tools and th...
New
xiji2646-netizen
Woke up to this today: Claude Code’s complete source code exposed via npm source map. Not a snippet. All 512,000 lines. 1,900 TypeScript ...
New

Latest in Functional Programming in Java, Second Edition

Functional Programming in Java, Second Edition Portal ❯

Sub Categories: