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

yulkin
your book suggests to use Image.toByteData() to convert image to bytes, however I get the following error: "the getter ‘toByteData’ isn’t...
New
raul
Hi Travis! Thank you for the cool book! :slight_smile: I made a list of issues and thought I could post them chapter by chapter. I’m rev...
New
jskubick
I’m under the impression that when the reader gets to page 136 (“View Data with the Database Inspector”), the code SHOULD be able to buil...
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
hazardco
On page 78 the following code appears: &lt;%= link_to ‘Destroy’, product, class: ‘hover:underline’, method: :delete, data: { confirm...
New
taguniversalmachine
Hi, I am getting an error I cannot figure out on my test. I have what I think is the exact code from the book, other than I changed “us...
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
tkhobbes
After some hassle, I was able to finally run bin/setup, now I have started the rails server but I get this error message right when I vis...
New
davetron5000
Hello faithful readers! If you have tried to follow along in the book, you are asked to start up the dev environment via dx/build and ar...
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

AstonJ
Or looking forward to? :nerd_face:
485 12328 258
New
Exadra37
I am thinking in building or buy a desktop computer for programing, both professionally and on my free time, and my choice of OS is Linux...
New
AstonJ
poll poll Be sure to check out @Dusty’s article posted here: An Introduction to Alternative Keyboard Layouts It’s one of the best write-...
New
AstonJ
Just done a fresh install of macOS Big Sur and on installing Erlang I am getting: asdf install erlang 23.1.2 Configure failed. checking ...
New
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
PragmaticBookshelf
Develop, deploy, and debug BEAM applications using BEAMOps: a new paradigm that focuses on scalability, fault tolerance, and owning each ...
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
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

Latest in Functional Programming in Java, Second Edition

Functional Programming in Java, Second Edition Portal

Sub Categories: