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\0as 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()));
}
}
Popular Pragmatic Bookshelf topics
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
Hi Jamis,
I think there’s an issue with a test on chapter 6. I own the ebook, version P1.0 Feb. 2019.
This test doesn’t pass for me:
...
New
Hi! I know not the intentions behind this narrative when called, on page XI:
mount() |> handle_event() |> render()
but the correc...
New
#book-python-testing-with-pytest-second-edition
Hi. Thanks for writing the book. I am just learning so this might just of been an issue ...
New
This is as much a suggestion as a question, as a note for others.
Locally the SGP30 wasn’t available, so I ordered a SGP40. On page 53, ...
New
Hi, I have just acquired Michael Fazio’s “Kotlin and Android Development” to learn about game programming for Android. I have a game in p...
New
I’m not quite sure what’s going on here, but I’m unable to have to containers successfully complete the Readiness/Liveness checks. I’m im...
New
When trying to run tox in parallel as explained on page 151, I got the following error:
tox: error: argument -p/–parallel: expected one...
New
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
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
Which, if any, games do you play? On what platform?
I just bought (and completed) Minecraft Dungeons for my Nintendo Switch. Other than ...
New
Start building native Android apps the modern way in Kotlin with Jetpack's expansive set of tools, libraries, and best practices. Learn h...
New
New
This looks like a stunning keycap set :orange_heart:
A LEGENDARY KEYBOARD LIVES ON
When you bought an Apple Macintosh computer in the e...
New
Do the test and post your score :nerd_face:
:keyboard:
If possible, please add info such as the keyboard you’re using, the layout (Qw...
New
I am asking for any distro that only has the bare-bones to be able to get a shell in the server and then just install the packages as we ...
New
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
Author Spotlight
Erin Dees
@undees
Welcome to our new author spotlight! We had the pleasure of chatting with Erin Dees, co-author of ...
New
Fight complexity and reclaim the original spirit of agility by learning to simplify how you develop software. The result: a more humane a...
New
A concise guide to MySQL 9 database administration, covering fundamental concepts, techniques, and best practices.
Neil Smyth
MySQL...
New
Categories:
Sub Categories:
Popular Portals
- /elixir
- /rust
- /wasm
- /ruby
- /erlang
- /phoenix
- /keyboards
- /python
- /js
- /rails
- /security
- /go
- /swift
- /vim
- /clojure
- /java
- /emacs
- /haskell
- /svelte
- /onivim
- /typescript
- /kotlin
- /c-plus-plus
- /crystal
- /tailwind
- /react
- /gleam
- /ocaml
- /flutter
- /elm
- /vscode
- /ash
- /html
- /opensuse
- /deepseek
- /zig
- /centos
- /php
- /scala
- /react-native
- /lisp
- /textmate
- /sublime-text
- /nixos
- /debian
- /agda
- /django
- /deno
- /kubuntu
- /arch-linux
- /nodejs
- /ubuntu
- /spring
- /revery
- /manjaro
- /julia
- /lua
- /diversity
- /markdown
- /slackware









