From 6743c4de492c5937f4b2807b6630fe4a1f4ab1cb Mon Sep 17 00:00:00 2001
From: Maciej Glowka <maciejglowka.pl@gmail.com>
Date: Fri, 20 Nov 2020 00:42:56 +0100
Subject: [PATCH] BAEL-4725: examples of double comparison in Java

---
 core-java-modules/core-java-lang-3/pom.xml    | 12 ++++
 .../comparedouble/CompareDoubleUnitTest.java  | 71 +++++++++++++++++++
 2 files changed, 83 insertions(+)
 create mode 100644 core-java-modules/core-java-lang-3/src/test/java/com/baeldung/comparedouble/CompareDoubleUnitTest.java

diff --git a/core-java-modules/core-java-lang-3/pom.xml b/core-java-modules/core-java-lang-3/pom.xml
index de290717b1..f98074ad1b 100644
--- a/core-java-modules/core-java-lang-3/pom.xml
+++ b/core-java-modules/core-java-lang-3/pom.xml
@@ -23,6 +23,18 @@
             <version>${assertj.version}</version>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>com.google.guava</groupId>
+            <artifactId>guava</artifactId>
+            <version>${guava.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-math3</artifactId>
+            <version>3.6.1</version>
+            <scope>test</scope>
+        </dependency>
     </dependencies>
 
     <build>
diff --git a/core-java-modules/core-java-lang-3/src/test/java/com/baeldung/comparedouble/CompareDoubleUnitTest.java b/core-java-modules/core-java-lang-3/src/test/java/com/baeldung/comparedouble/CompareDoubleUnitTest.java
new file mode 100644
index 0000000000..c70dabd014
--- /dev/null
+++ b/core-java-modules/core-java-lang-3/src/test/java/com/baeldung/comparedouble/CompareDoubleUnitTest.java
@@ -0,0 +1,71 @@
+package com.baeldung.comparedouble;
+
+import com.google.common.math.DoubleMath;
+import org.apache.commons.math3.util.Precision;
+import org.junit.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.junit.Assert.assertEquals;
+
+public class CompareDoubleUnitTest {
+
+    @Test
+    public void givenDoubleValuesThatShouldHaveSameValue_whenUsingSimpleComparison_thenFails() {
+        double d1 = getFirstDouble(0);
+
+        double d2 = .1 * 8;
+
+        assertThat(d1 == d2).isFalse();
+    }
+
+    @Test
+    public void givenDoubleValuesThatShouldHaveSameValue_whenUsingThresholdComparison_thenSuccess() {
+        double d1 = getFirstDouble(0);
+
+        double d2 = .1 * 8;
+
+        double epsilon = 0.000001d;
+
+        assertThat(Math.abs(d1 - d2) < epsilon).isTrue();
+    }
+
+    @Test
+    public void givenDoubleValuesThatShouldHaveSameValue_whenUsingGuavaFuzzyComparison_thenSuccess() {
+        double d1 = getFirstDouble(0);
+        double d2 = .1 * 8;
+
+        double epsilon = 0.000001d;
+
+
+        assertThat(DoubleMath.fuzzyEquals(d1, d2, epsilon)).isTrue();
+    }
+
+    @Test
+    public void givenDoubleValuesThatShouldHaveSameValue_whenUsingCommonsMathComparison_thenSuccess() {
+        double d1 = getFirstDouble(0);
+        double d2 = .1 * 8;
+
+        double epsilon = 0.000001d;
+
+
+        assertThat(Precision.equals(d1, d2, epsilon)).isTrue();
+        assertThat(Precision.equals(d1, d2)).isTrue();
+    }
+
+    @Test
+    public void givenDoubleValuesThatShouldHaveSameValue_whenUsingJunitComparison_thenSuccess() {
+        double d1 = getFirstDouble(0);
+        double d2 = .1 * 8;
+
+        double epsilon = 0.000001d;
+
+        assertEquals(d1, d2, epsilon);
+    }
+
+    private double getFirstDouble(double d1) {
+        for (int i = 1; i <= 8; i++) {
+            d1 += .1;
+        }
+        return d1;
+    }
+}
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