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
Title: Design and Build Great Web APIs - typo “https://company-atk.herokuapp.com/2258ie4t68jv” (page 19, third bullet in URL list)
Typo:...
New
I am working on the “Your Turn” for chapter one and building out the restart button talked about on page 27. It recommends looking into ...
New
When installing Cards as an editable package, I get the following error:
ERROR: File “setup.py” not found. Directory cannot be installe...
New
Hey there,
I’m enjoying this book and have learned a few things alredayd. However, in Chapter 4 I believe we are meant to see the “>...
New
On page 78 the following code appears:
<%= link_to ‘Destroy’, product,
class: ‘hover:underline’,
method: :delete,
data: { confirm...
New
I’m a newbie to Rails 7 and have hit an issue with the bin/Dev script mentioned on pages 112-113.
Iteration A1 - Seeing the list of prod...
New
The allprojects block listed on page 245 produces the following error when syncing gradle:
“org.gradle.api.GradleScriptException: A prob...
New
@parrt
In the context of Chapter 4.3, the grammar Java.g4, meant to parse Java 6 compilation units, no longer passes ANTLR (currently 4....
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
Other popular topics
New
No chair. I have a standing desk.
This post was split into a dedicated thread from our thread about chairs :slight_smile:
New
Curious to know which languages and frameworks you’re all thinking about learning next :upside_down_face:
Perhaps if there’s enough peop...
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
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
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
Saw this on TikTok of all places! :lol:
Anyone heard of them before?
Lite:
New
Author Spotlight
Jamis Buck
@jamis
This month, we have the pleasure of spotlighting author Jamis Buck, who has written Mazes for Prog...
New
Inside our android webview app, we are trying to paste the copied content from another app eg (notes) using navigator.clipboard.readtext ...
New
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
Categories:
Sub Categories:
Popular Portals
- /elixir
- /rust
- /ruby
- /wasm
- /erlang
- /phoenix
- /keyboards
- /python
- /js
- /rails
- /security
- /go
- /swift
- /vim
- /clojure
- /emacs
- /java
- /haskell
- /svelte
- /onivim
- /typescript
- /kotlin
- /crystal
- /c-plus-plus
- /tailwind
- /react
- /gleam
- /ocaml
- /elm
- /flutter
- /vscode
- /ash
- /html
- /opensuse
- /centos
- /zig
- /deepseek
- /php
- /scala
- /react-native
- /sublime-text
- /lisp
- /textmate
- /debian
- /nixos
- /agda
- /kubuntu
- /django
- /arch-linux
- /deno
- /ubuntu
- /revery
- /nodejs
- /spring
- /manjaro
- /lua
- /diversity
- /markdown
- /julia
- /slackware








