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

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
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
cro
I am working on the “Your Turn” for chapter one and building out the restart button talked about on page 27. It recommends looking into ...
New
New
oaklandgit
Hi, I completed chapter 6 but am getting the following error when running: thread 'main' panicked at 'Failed to load texture: IoError(O...
New
creminology
Skimming ahead, much of the following is explained in Chapter 3, but new readers (like me!) will hit a roadblock in Chapter 2 with their ...
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
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
mcpierce
@mfazio23 I’ve applied the changes from Chapter 5 of the book and everything builds correctly and runs. But, when I try to start a game,...
New
roadbike
From page 13: On Python 3.7, you can install the libraries with pip by running these commands inside a Python venv using Visual Studio ...
New

Other popular topics Top

Devtalk
Hello Devtalk World! Please let us know a little about who you are and where you’re from :nerd_face:
New
Exadra37
Please tell us what is your preferred monitor setup for programming(not gaming) and why you have chosen it. Does your monitor have eye p...
New
Rainer
My first contact with Erlang was about 2 years ago when I used RabbitMQ, which is written in Erlang, for my job. This made me curious and...
New
PragmaticBookshelf
Rust is an exciting new programming language combining the power of C with memory safety, fearless concurrency, and productivity boosters...
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
PragmaticBookshelf
Use WebRTC to build web applications that stream media and data in real time directly from one user to another, all in the browser. ...
New
First poster: bot
zig/http.zig at 7cf2cbb33ef34c1d211135f56d30fe23b6cacd42 · ziglang/zig. General-purpose programming language and toolchain for maintaini...
New
AstonJ
This is a very quick guide, you just need to: Download LM Studio: https://lmstudio.ai/ Click on search Type DeepSeek, then select the o...
New
PragmaticBookshelf
Escape callback hell and ship fast, clean code that reads as smoothly as it runs. Squash bugs and stamp out memory leaks with an intuitiv...
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: