add using collection.max (#17864)

Author: wynnteo

core-java-modules/core-java-streams-4/src/main/java/com/baeldung/streams/maxdate/DateHelper.java

@@ -1,9 +1,11 @@
 package com.baeldung.streams.maxdate;
 
 import java.time.LocalDate;
+import java.util.Collections;
 import java.util.Comparator;
 import java.util.Date;
 import java.util.List;
+import java.util.stream.Collectors;
 
 public class DateHelper {
 
@@ -87,4 +89,21 @@ static final LocalDate findMinDateOfLocalEventsWithComparator(List<LocalEvent> e
             .get();
     }
 
+    static Date findMaxDateWithCollections(List<Event> events) {
+        if (events == null || events.isEmpty()) {
+            return null;
+        }
+        return Collections.max(events.stream()
+            .map(Event::getDate)
+            .collect(Collectors.toList()));
+    }
+
+    static LocalDate findMaxLocalDateWithCollections(List<LocalEvent> events) {
+        if (events == null || events.isEmpty()) {
+            return null;
+        }
+        return Collections.max(events.stream()
+            .map(LocalEvent::getDate)
+            .collect(Collectors.toList()));
+    }
 }

core-java-modules/core-java-streams-4/src/test/java/com/baeldung/streams/maxdate/DateHelperUnitTest.java

@@ -186,5 +186,13 @@ void givenLocalEventList_whenFindMinDateOfLocalEventsWithComparator_thenReturnMa
         assertEquals(TODAY_LOCAL, DateHelper.findMinDateOfLocalEventsWithComparator(List.of(TODAY_LOCAL_EVENT, TOMORROW_LOCAL_EVENT, NEXT_WEEK_LOCAL_EVENT)));
     }
 
-    
+    @Test
+    void givenEventList_whenFindMaxDateWithCollections_thenReturnMaxDate() {
+        assertEquals(NEXT_WEEK, DateHelper.findMaxDateWithCollections(List.of(TODAYS_EVENT, TOMORROWS_EVENT, NEXT_WEEK_EVENT)));
+    }
+
+    @Test
+    void givenLocalEventList_whenFindMaxLocalDateWithCollections_thenReturnMaxDate() {
+        assertEquals(NEXT_WEEK_LOCAL, DateHelper.findMaxLocalDateWithCollections(List.of(TODAY_LOCAL_EVENT, TOMORROW_LOCAL_EVENT, NEXT_WEEK_LOCAL_EVENT)));
+    }
 }