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

abtin
page 20: … protoc command… I had to additionally run the following go get commands in order to be able to compile protobuf code using go...
New
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
herminiotorres
Hi @Margaret , On page VII the book tells us the example and snippets will be all using Elixir version 1.11 But on page 3 almost the en...
New
Chrichton
Dear Sophie. I tried to do the “Authorization” exercise and have two questions: When trying to plug in an email-service, I found the ...
New
jskubick
I think I might have found a problem involving SwitchCompat, thumbTint, and trackTint. As entered, the SwitchCompat changes color to hol...
New
jskubick
I found an issue in Chapter 7 regarding android:backgroundTint vs app:backgroundTint. How to replicate: load chapter-7 from zipfile i...
New
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
andreheijstek
After running /bin/setup, the first error was: The foreman' command exists in these Ruby versions: That was easy to fix: gem install fore...
New
SlowburnAZ
Getting an error when installing the dependencies at the start of this chapter: could not compile dependency :exla, "mix compile" failed...
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
AstonJ
In case anyone else is wondering why Ruby 3 doesn’t show when you do asdf list-all ruby :man_facepalming: do this first: asdf plugin-upd...
New
PragmaticBookshelf
Create efficient, elegant software tests in pytest, Python's most powerful testing framework. Brian Okken @brianokken Edited by Kat...
New
foxtrottwist
A few weeks ago I started using Warp a terminal written in rust. Though in it’s current state of development there are a few caveats (tab...
New
PragmaticBookshelf
Rails 7 completely redefines what it means to produce fantastic user experiences and provides a way to achieve all the benefits of single...
New
PragmaticBookshelf
Author Spotlight Rebecca Skinner @RebeccaSkinner Welcome to our latest author spotlight, where we sit down with Rebecca Skinner, auth...
New
New
New
PragmaticBookshelf
Explore the power of Ash Framework by modeling and building the domain for a real-world web application. Rebecca Le @sevenseacat and ...
New
AstonJ
Curious what kind of results others are getting, I think actually prefer the 7B model to the 32B model, not only is it faster but the qua...
New

Latest in Functional Programming in Java, Second Edition

Functional Programming in Java, Second Edition Portal

Sub Categories: