AssertJ SoftAssertions JavaDoc

I recently came across a great example of JavaDoc. It was regarding the AssertJ SoftAssertions class.

It's in the references¹.

In short, we have a dinner party hosted at a mansion.

And we're going to use a UnitTest with Assertions to determine if one of the guests has been murdered and who dun it.

It made me smile.

References

[1] SoftAssertions - AssertJ fluent assertions 3.16.1 API

https://www.javadoc.io/doc/org.assertj/assertj-core/latest/org/assertj/core/api/SoftAssertions.html

Kotlin

I am busy trying to learn Kotlin.

It's important as my company decided to accept the use of Kotlin for new development.

As a matter of fact, I'm currently implementing an API with a colleague and he already started creating it in Kotlin.

So I'm kinda having to play catchup.

Time to get to work!

References

Kotlin Language Guide

https://kotlinlang.org/docs/reference/

Kotlin Koans

https://kotlinlang.org/docs/tutorials/koans.html

What I learned about Java from my 5-year old.

So, you're at home all day, because of all the COVID stuff, and in order to stay sane, you sometimes have to do things that are out of the ordinary.

Below is my attempt.

The Dangers of Doubles

The problems with Doubles and Floats are already well documented, but sometimes we fall into the trap again.

In short, the representation of a real number¹ in Float and Double is not precise².

Normally, I am well aware of this limitation, but sometimes I get tripped up by already receiving Doubles and Floats as input.

In this case, it involved Geometrie coordinates, in doubles of course.

The following Unit Test shows the problem:

	package com.mrbear;
	import org.testng.annotations.Test;
	import java.math.BigDecimal;
	import java.math.RoundingMode;
	import java.text.NumberFormat;
	import java.util.Locale;
	import static org.assertj.core.api.Java6Assertions.assertThat;
	public class Arithmetic {
	@Test
	public void testRoundingSpecial() {
	Double x = 89026.1415;
	Double y = 469041.5955;
	NumberFormat nf = NumberFormat.getInstance(Locale.ENGLISH);
	nf.setMinimumFractionDigits(3);
	nf.setRoundingMode(RoundingMode.HALF_UP);
	nf.setGroupingUsed(false);
	assertThat(new BigDecimal(x)).isEqualTo(new BigDecimal("89026.14149999999790452420711517333984375"));
	assertThat(new BigDecimal(y)).isEqualTo(new BigDecimal("469041.5954999999958090484142303466796875"));
	// assertThat(nf.format(x)).isEqualTo("89026.142"); // this fails, because 89026.14149 will be rounded DOWN!
	assertThat(nf.format(x)).isEqualTo("89026.141");
	// assertThat(nf.format(y)).isEqualTo("469041.596"); // // this fails, because 469041.595499 will be rounded DOWN!
	assertThat(nf.format(y)).isEqualTo("469041.595");
	}
	@Test
	public void testRoundingNotSpecial() {
	Double x = 72542.6245;
	Double y = 447798.0295;
	NumberFormat nf = NumberFormat.getInstance(Locale.ENGLISH);
	nf.setMinimumFractionDigits(3);
	nf.setRoundingMode(RoundingMode.HALF_UP);
	nf.setGroupingUsed(false);
	assertThat(new BigDecimal(x)).isEqualTo(new BigDecimal("72542.62450000000535510480403900146484375"));
	assertThat(new BigDecimal(y)).isEqualTo(new BigDecimal("447798.0295000000041909515857696533203125"));
	assertThat(nf.format(x)).isEqualTo("72542.625");
	assertThat(nf.format(y)).isEqualTo("447798.030");
	}
	}

view raw Arithmetic.java hosted with ❤ by GitHub

References

[1] Wikipedia - Real number

https://en.wikipedia.org/wiki/Real_number

[2] What Every Programmer Should Know About Floating-Point Arithmetic

https://floating-point-gui.de/