BAEL-3130 overflow and underflow in java (#8381)

* BAEL-3131 Guide to Java HashMap
http://jira.baeldung.com/browse/BAEL-3130

* Move test class to correct package
http://jira.baeldung.com/browse/BAEL-3130

core-java-modules/core-java-lang-math/src/test/java/com/baeldung/overflow/OverflowUnitTest.java

@@ -0,0 +1,22 @@
+package com.baeldung.overflow;
+
+import static org.junit.Assert.assertTrue;
+
+import org.junit.Test;
+
+public class OverflowUnitTest {
+
+    @Test
+    public void positive_and_negative_zero_are_not_always_equal() {
+
+        double a = +0f;
+        double b = -0f;
+
+        assertTrue(a == b);
+
+        assertTrue(1/a == Double.POSITIVE_INFINITY);
+        assertTrue(1/b == Double.NEGATIVE_INFINITY);
+
+        assertTrue(1/a != 1/b);
+    }
+}