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
Running the examples in chapter 5 c under pytest 5.4.1 causes an AttributeError: ‘module’ object has no attribute ‘config’.
In particula...
New
Many tasks_proj/tests directories exist in chapters 2, 3, 5 that have tests that use the custom markers smoke and get, which are not decl...
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
Hello! On page xix of the preface, it says there is a community forum "… for help if your’re stuck on one of the exercises in this book… ...
New
The book has the same “Problem space/Solution space” diagram on page 18 as is on page 17. The correct Problem/Solution space diagrams ar...
New
@noelrappin
Running the webpack dev server, I receive the following warning:
ERROR in tsconfig.json
TS18003: No inputs were found in c...
New
In general, the book isn’t yet updated for Phoenix version 1.6. On page 18 of the book, the authors indicate that an auto generated of ro...
New
I got this error when executing the plot files on macOS Ventura 13.0.1 with Python 3.10.8 and matplotlib 3.6.1:
programming_ML/code/03_...
New
@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
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
Other popular topics
Brace yourself for a fun challenge: build a photorealistic 3D renderer from scratch! In just a couple of weeks, build a ray tracer that r...
New
New
You might be thinking we should just ask who’s not using VSCode :joy: however there are some new additions in the space that might give V...
New
My first contact with Erlang was about 2 years ago when I used RabbitMQ, which is written in Erlang, for my job. This made me curious and...
New
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
We have a thread about the keyboards we have, but what about nice keyboards we come across that we want? If you have seen any that look n...
New
I ended up cancelling my Moonlander order as I think it’s just going to be a bit too bulky for me.
I think the Planck and the Preonic (o...
New
This is going to be a long an frequently posted thread.
While talking to a friend of mine who has taken data structure and algorithm cou...
New
Use advanced functional programming principles, practical Domain-Driven Design techniques, and production-ready Elixir code to build scal...
New
Woke up to this today: Claude Code’s complete source code exposed via npm source map. Not a snippet. All 512,000 lines. 1,900 TypeScript ...
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
- /deepseek
- /zig
- /centos
- /php
- /scala
- /react-native
- /lisp
- /textmate
- /sublime-text
- /nixos
- /debian
- /agda
- /deno
- /django
- /kubuntu
- /arch-linux
- /nodejs
- /spring
- /ubuntu
- /revery
- /manjaro
- /lua
- /julia
- /diversity
- /markdown
- /c









