BAEL-4725: examples of double comparison in Java

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;
+    }
+}