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
Title: Design and Build Great Web APIs - typo “https://company-atk.herokuapp.com/2258ie4t68jv” (page 19, third bullet in URL list)
Typo:...
New
Hi! I know not the intentions behind this narrative when called, on page XI:
mount() |> handle_event() |> render()
but the correc...
New
Title: Intuitive Python: docker run… denied error (page 2)
Attempted to run the docker command in both CLI and Powershell
PS C:\Users\r...
New
I’m running Android Studio “Arctic Fox” 2020.3.1 Patch 2, and I’m embarrassed to admit that I only made it to page 8 before running into ...
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
On page 78 the following code appears:
<%= link_to ‘Destroy’, product,
class: ‘hover:underline’,
method: :delete,
data: { confirm...
New
The markup used to display the uploaded image results in a Phoenix.LiveView.HTMLTokenizer.ParseError error.
lib/pento_web/live/product_l...
New
Book: Programming Phoenix LiveView, page 142 (157/378), file lib/pento_web/live/product_live/form_component.ex, in the function below:
d...
New
Hello @herbert ! Trying to get the very first “Hello, Bracket Terminal!" example to run (p. 53). I develop on an Amazon EC2 instance runn...
New
I’ve got to the end of Ch. 11, and the app runs, with all tabs displaying what they should – at first. After switching around between St...
New
Other popular topics
Hello Devtalk World!
Please let us know a little about who you are and where you’re from :nerd_face:
New
Ruby, Io, Prolog, Scala, Erlang, Clojure, Haskell. With Seven Languages in Seven Weeks, by Bruce A. Tate, you’ll go beyond the syntax—and...
New
I know that these benchmarks might not be the exact picture of real-world scenario, but still I expect a Rust web framework performing a ...
New
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
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
Hi folks,
I don’t know if I saw this here but, here’s a new programming language, called Roc
Reminds me a bit of Elm and thus Haskell. ...
New
Author Spotlight
Dmitry Zinoviev
@aqsaqal
Today we’re putting our spotlight on Dmitry Zinoviev, author of Data Science Essentials in ...
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
New
Use advanced functional programming principles, practical Domain-Driven Design techniques, and production-ready Elixir code to build scal...
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
- /elm
- /flutter
- /vscode
- /ash
- /html
- /opensuse
- /zig
- /centos
- /deepseek
- /php
- /scala
- /react-native
- /lisp
- /sublime-text
- /textmate
- /nixos
- /debian
- /agda
- /deno
- /django
- /kubuntu
- /arch-linux
- /nodejs
- /ubuntu
- /spring
- /revery
- /manjaro
- /lua
- /julia
- /diversity
- /markdown
- /slackware









