BAEL-1074 Difference between two dates in Java (#2493)

* Different types of bean injection in Spring

* Difference between two dates in java

* Update README.md

* Simple clean of difference between dates

* Clean my test article

java-difference-date/src/test/java/com/baeldung/DateDiffTest.java

@@ -0,0 +1,61 @@
+package com.baeldung;
+
+import org.joda.time.DateTime;
+import org.junit.Test;
+
+import java.text.ParseException;
+import java.text.SimpleDateFormat;
+import java.time.Duration;
+import java.time.ZonedDateTime;
+import java.util.Date;
+import java.util.Locale;
+import java.util.TimeZone;
+import java.util.concurrent.TimeUnit;
+
+import static org.junit.Assert.assertEquals;
+
+public class DateDiffTest {
+    @Test
+    public void givenTwoDatesBeforeJava8_whenDifferentiating_thenWeGetSix() throws ParseException {
+        SimpleDateFormat sdf = new SimpleDateFormat("MM/dd/yyyy", Locale.ENGLISH);
+        Date firstDate = sdf.parse("06/24/2017");
+        Date secondDate = sdf.parse("06/30/2017");
+
+        long diffInMillies = Math.abs(secondDate.getTime() - firstDate.getTime());
+        long diff = TimeUnit.DAYS.convert(diffInMillies, TimeUnit.MILLISECONDS);
+
+        assertEquals(diff, 6);
+    }
+
+    @Test
+    public void givenTwoDatesInJava8_whenDifferentiating_thenWeGetSix() {
+        ZonedDateTime now = ZonedDateTime.now();
+        ZonedDateTime sixDaysBehind = now.minusDays(6);
+
+        Duration duration = Duration.between(now, sixDaysBehind);
+        long diff = Math.abs(duration.toDays());
+
+        assertEquals(diff, 6);
+    }
+
+    @Test
+    public void givenTwoDatesInJodaTime_whenDifferentiating_thenWeGetSix() {
+        DateTime now = DateTime.now();
+        DateTime sixDaysBehind = now.minusDays(6);
+
+        org.joda.time.Duration duration = new org.joda.time.Duration(now, sixDaysBehind);
+        long diff = Math.abs(duration.getStandardDays());
+
+        assertEquals(diff, 6);
+    }
+
+    @Test
+    public void givenTwoDatesInDate4j_whenDifferentiating_thenWeGetSix() {
+        hirondelle.date4j.DateTime now = hirondelle.date4j.DateTime.now(TimeZone.getDefault());
+        hirondelle.date4j.DateTime sixDaysBehind = now.minusDays(6);
+
+        long diff = Math.abs(now.numDaysFrom(sixDaysBehind));
+
+        assertEquals(diff, 6);
+    }
+}