Add a double comparator (#17273)

Author: wynnteo

core-java-modules/core-java-lang-3/src/main/java/com/baeldung/comparedouble/DoubleComparator.java

@@ -0,0 +1,22 @@
+package com.baeldung.comparedouble;
+
+import java.util.Comparator;
+
+public class DoubleComparator implements Comparator<Double> {
+    private double epsilon;
+
+    public DoubleComparator(double epsilon) {
+        this.epsilon = epsilon;
+    }
+
+    @Override
+    public int compare(Double d1, Double d2) {
+        if (Math.abs(d1 - d2) < epsilon) {
+            return 0; // equal
+        } else if (d1 < d2) {
+            return -1; // d1 is less than d2
+        } else {
+            return 1; // d1 is greater than d2
+        }
+    }
+}

core-java-modules/core-java-lang-3/src/test/java/com/baeldung/comparedouble/CompareDoubleUnitTest.java

@@ -68,4 +68,13 @@ private double getFirstDouble(double d1) {
         }
         return d1;
     }
+
+    @Test
+    public void givenTwoEqualDoubleValues_whenUseComparator_thenReturnsZero() {
+        double d1 = getFirstDouble(0);
+        double d2 = .1 * 8;
+        DoubleComparator comparator = new DoubleComparator(0.000001d);
+        int result = comparator.compare(d1, d2);
+        assertEquals(0, result);
+    }
 }