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
your book suggests to use Image.toByteData() to convert image to bytes, however I get the following error: "the getter ‘toByteData’ isn’t...
New
Title: Hands-On Rust (Chapter 11: prefab)
Just played a couple of amulet-less games. With a bit of debugging, I believe that your can_p...
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
Title: Web Development with Clojure, Third Edition, vB17.0 (p9)
The create table guestbook syntax suggested doesn’t seem to be accepted ...
New
In case this helps anyone, I’ve had issues setting up the rails source code. Here were the solutions:
In Gemfile, change
gem 'rails'
t...
New
I think I might have found a problem involving SwitchCompat, thumbTint, and trackTint.
As entered, the SwitchCompat changes color to hol...
New
“The ProductLive.Index template calls a helper function, live_component/3, that in turn calls on the modal component. ”
Excerpt From: Br...
New
AWDWR 7, page 152, page 153:
Hello everyone,
I’m a little bit lost on the hotwire part. I didn’t fully understand it.
On page 152 @rub...
New
Other popular topics
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
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
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
Small essay with thoughts on macOS vs. Linux:
I know @Exadra37 is just waiting around the corner to scream at me “I TOLD YOU SO!!!” but I...
New
Learn different ways of writing concurrent code in Elixir and increase your application's performance, without sacrificing scalability or...
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
If you get Can't find emacs in your PATH when trying to install Doom Emacs on your Mac you… just… need to install Emacs first! :lol:
bre...
New
Author Spotlight
Rebecca Skinner
@RebeccaSkinner
Welcome to our latest author spotlight, where we sit down with Rebecca Skinner, auth...
New
Jan | Rethink the Computer.
Jan turns your computer into an AI machine by running LLMs locally on your computer. It’s a privacy-focus, l...
New
Categories:
Sub Categories:
Popular Portals
- /elixir
- /rust
- /wasm
- /ruby
- /erlang
- /phoenix
- /keyboards
- /python
- /js
- /rails
- /security
- /go
- /swift
- /vim
- /clojure
- /emacs
- /haskell
- /java
- /svelte
- /onivim
- /typescript
- /kotlin
- /crystal
- /c-plus-plus
- /tailwind
- /react
- /gleam
- /ocaml
- /elm
- /flutter
- /vscode
- /ash
- /html
- /opensuse
- /zig
- /centos
- /deepseek
- /php
- /scala
- /react-native
- /lisp
- /textmate
- /sublime-text
- /nixos
- /debian
- /agda
- /django
- /deno
- /kubuntu
- /arch-linux
- /nodejs
- /revery
- /ubuntu
- /manjaro
- /spring
- /lua
- /diversity
- /julia
- /markdown
- /c








