dtonhofer

dtonhofer

Functional Programming in Java, Second Edition: Functional Programming in Java, Second Edition: JUnit code improvements for Chapter 11, pages 189 ff “Refactoring to Rework the Logic”

The usual changes but:

  • The “FirstRepeatedLetter.findIn()” has been improved out of the box. In particular returning ‘\0’ is too C-like and smells like “primitive obsession”. We have null, we should use it. What if the input contains \0 as the matching character?
  • A slightly better code (IMHO) is in FirstRepeatedLetterBetter.findIn()
  • The final refactored code returns not null, but Optional<Character>, which is cleaner.
  • Again, for testing we use a common interface or a wrapper class to avoid having to duplicate testing code.
package chapter11;

import org.junit.jupiter.api.Test;

import java.util.Optional;
import java.util.stream.Stream;

import static org.junit.jupiter.api.Assertions.*;

public class ReworkTheLogicTest {

    interface FindLetter {

        Character findIn(String word);

    }

    static class FirstRepeatedLetterBefore implements FindLetter {

        public Character findIn(final String word) {
            final char[] letters = word.toCharArray();
            for (char candidate : letters) {
                int count = 0;
                for (char letter : letters) {
                    if (candidate == letter) {
                        count++;
                    }
                }
                if (count > 1) {
                    return candidate;
                }
            }
            return null;
        }
    }

    static class FirstRepeatedLetterBetter implements FindLetter {

        public Character findIn(final String word) {
            char[] letters = word.toCharArray();
            int i = 0;
            Character found = null;
            while (i < letters.length && found == null) {
                // will letter[i] been seen again?
                char maybe = letters[i];
                int j = i + 1;
                while (j < letters.length && letters[j] != maybe) j++;
                if (j < letters.length) {
                    found = maybe;
                } else {
                    i++;
                }
            }
            return found;
        }
    }

    // Does NOT implement "FindLetter", returns Optional<Character>

    static class FirstRepeatedLetterAfter {

        public Optional<Character> findIn(final String word) {
            return Stream.of(word.split(""))
                    .filter(letter -> word.lastIndexOf(letter) > word.indexOf(letter))
                    .findFirst()
                    .map(letter -> letter.charAt(0));
        }
    }

    static class FirstRepeatedLetterAfterWrapped implements FindLetter {

        private final FirstRepeatedLetterAfter finder;

        public FirstRepeatedLetterAfterWrapped(FirstRepeatedLetterAfter finder) {
            this.finder = finder;
        }

        public Character findIn(final String word) {
            return finder.findIn(word).orElse(null);
        }
    }

    private static void commonFindFirstRepeatingTests(final FindLetter finder) {
        assertAll(
                () -> assertEquals('l', finder.findIn("hello")),
                () -> assertEquals('h', finder.findIn("hellothere")),
                () -> assertEquals('a', finder.findIn("magicalguru")),
                () -> assertEquals('z', finder.findIn("abcdefghijklmnopqrstuvwxyzz")),
                () -> assertNull(finder.findIn("once")),
                () -> assertNull(finder.findIn(""))
        );
    }

    @Test
    void findFirstRepeatingBefore() {
        commonFindFirstRepeatingTests(new FirstRepeatedLetterBefore());
    }

    @Test
    void findFirstRepeatingBetter() {
        commonFindFirstRepeatingTests(new FirstRepeatedLetterBetter());
    }

    @Test
    void findFirstRepeatingAfter() {
        commonFindFirstRepeatingTests(new FirstRepeatedLetterAfterWrapped(new FirstRepeatedLetterAfter()));
    }

}

Where Next?

Popular Pragmatic Bookshelf topics Top

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 think I might have found a problem involving SwitchCompat, thumbTint, and trackTint. As entered, the SwitchCompat changes color to hol...
New
digitalbias
Title: Build a Weather Station with Elixir and Nerves: Problem connecting to Postgres with Grafana on (page 64) If you follow the defau...
New
dsmith42
Hey there, I’m enjoying this book and have learned a few things alredayd. However, in Chapter 4 I believe we are meant to see the “&gt;...
New
akraut
The markup used to display the uploaded image results in a Phoenix.LiveView.HTMLTokenizer.ParseError error. lib/pento_web/live/product_l...
New
s2k
Hi all, currently I wonder how the Tailwind colours work (or don’t work). For example, in app/views/layouts/application.html.erb I have...
New
Henrai
Hi, I’m working on the Chapter 8 of the book. After I add add the point_offset, I’m still able to see acne: In the image above, I re...
New
New
gorkaio
root_layout: {PentoWeb.LayoutView, :root}, This results in the following following error: no “root” html template defined for PentoWeb...
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

Other popular topics Top

PragmaticBookshelf
Free and open source software is the default choice for the technologies that run our world, and it’s built and maintained by people like...
New
ohm
Which, if any, games do you play? On what platform? I just bought (and completed) Minecraft Dungeons for my Nintendo Switch. Other than ...
New
AstonJ
Or looking forward to? :nerd_face:
498 13326 269
New
DevotionGeo
I know that -t flag is used along with -i flag for getting an interactive shell. But I cannot digest what the man page for docker run com...
New
Help
I am trying to crate a game for the Nintendo switch, I wanted to use Java as I am comfortable with that programming language. Can you use...
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
AstonJ
This is cool! DEEPSEEK-V3 ON M4 MAC: BLAZING FAST INFERENCE ON APPLE SILICON We just witnessed something incredible: the largest open-s...
New
PragmaticBookshelf
Fight complexity and reclaim the original spirit of agility by learning to simplify how you develop software. The result: a more humane a...
New
PragmaticBookshelf
A concise guide to MySQL 9 database administration, covering fundamental concepts, techniques, and best practices. Neil Smyth MySQL...
New
PragmaticBookshelf
Use advanced functional programming principles, practical Domain-Driven Design techniques, and production-ready Elixir code to build scal...
New

Latest in Functional Programming in Java, Second Edition

Functional Programming in Java, Second Edition Portal

Sub Categories: