Iterate through a range of Dates in Java (#4959)

* Iterating over collection of dates

* Development of range dates iteration

* Removed some tests

* After editor review

* Unused interface removed

* Second code revision

core-java-9/src/main/java/com/baeldung/java9/rangedates/DatesCollectionIteration.java

@@ -0,0 +1,24 @@
+package com.baeldung.java9.rangedates;
+
+import java.util.Collection;
+import java.util.Date;
+
+public class DatesCollectionIteration {
+
+    public void iteratingRangeOfDatesJava7(Collection<Date> dates) {
+
+        for (Date date : dates) {
+            processDate(date);
+        }
+    }
+
+    public void iteratingRangeOfDatesJava8(Collection<Date> dates) {
+        dates.stream()
+            .forEach(this::processDate);
+    }
+
+    private void processDate(Date date) {
+        System.out.println(date);
+    }
+
+}

core-java-9/src/main/java/com/baeldung/java9/rangedates/RangeDatesIteration.java

@@ -0,0 +1,43 @@
+package com.baeldung.java9.rangedates;
+
+import java.time.LocalDate;
+import java.util.Calendar;
+import java.util.Date;
+
+public class RangeDatesIteration {
+
+    public void iterateBetweenDatesJava9(LocalDate startDate, LocalDate endDate) {
+
+        startDate.datesUntil(endDate)
+            .forEach(this::processDate);
+    }
+
+    public void iterateBetweenDatesJava8(LocalDate start, LocalDate end) {
+        for (LocalDate date = start; date.isBefore(end); date = date.plusDays(1)) {
+            processDate(date);
+        }
+    }
+
+    public void iterateBetweenDatesJava7(Date start, Date end) {
+        Date current = start;
+
+        while (current.before(end)) {
+            processDate(current);
+
+            Calendar calendar = Calendar.getInstance();
+            calendar.setTime(current);
+
+            calendar.add(Calendar.DATE, 1);
+
+            current = calendar.getTime();
+        }
+    }
+
+    private void processDate(LocalDate date) {
+        System.out.println(date);
+    }
+
+    private void processDate(Date date) {
+        System.out.println(date);
+    }
+}

core-java-9/src/test/java/com/baeldung/java9/rangedates/DatesCollectionIterationUnitTest.java

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+package com.baeldung.java9.rangedates;
+
+import java.time.LocalDate;
+import java.time.ZoneId;
+import java.time.temporal.ChronoUnit;
+import java.util.ArrayList;
+import java.util.Calendar;
+import java.util.Collection;
+import java.util.Date;
+import java.util.List;
+import java.util.stream.Collectors;
+
+import org.junit.Test;
+
+public class DatesCollectionIterationUnitTest {
+
+    private Collection<LocalDate> localDates = LocalDate.now()
+        .datesUntil(LocalDate.now()
+            .plus(10L, ChronoUnit.DAYS))
+        .collect(Collectors.toList());
+
+    private Collection<Date> dates = localDates.stream()
+        .map(localDate -> Date.from(localDate.atStartOfDay(ZoneId.systemDefault())
+            .toInstant()))
+        .collect(Collectors.toList());
+
+    @Test
+    public void givenIteratingListOfDatesJava7_WhenStartTodayAndEnding10DaysAhead() {
+        DatesCollectionIteration iterateInColleciton = new DatesCollectionIteration();
+        Calendar today = Calendar.getInstance();
+        Calendar next10Ahead = (Calendar) today.clone();
+        next10Ahead.add(Calendar.DATE, 10);
+
+        iterateInColleciton.iteratingRangeOfDatesJava7(createRangeDates(today.getTime(), next10Ahead.getTime()));
+    }
+
+    @Test
+    public void givenIteratingListOfDatesJava8_WhenStartTodayAndEnd10DaysAhead() {
+        DatesCollectionIteration iterateInColleciton = new DatesCollectionIteration();
+
+        iterateInColleciton.iteratingRangeOfDatesJava8(dates);
+    }
+
+    private List<Date> createRangeDates(Date start, Date end) {
+
+        List<Date> dates = new ArrayList<>();
+        Date current = start;
+
+        while (current.before(end)) {
+            dates.add(current);
+            
+            Calendar calendar = Calendar.getInstance();
+            calendar.setTime(current);
+            calendar.add(Calendar.DATE, 1);
+
+            current = calendar.getTime();
+        }
+
+        return dates;
+    }
+}

core-java-9/src/test/java/com/baeldung/java9/rangedates/RangeDatesIterationUnitTest.java

@@ -0,0 +1,48 @@
+package com.baeldung.java9.rangedates;
+
+import java.time.LocalDate;
+import java.time.temporal.ChronoUnit;
+import java.util.Calendar;
+import java.util.Date;
+
+import org.junit.Test;
+
+public class RangeDatesIterationUnitTest {
+
+    @Test
+    public void givenIterateBetweenDatesJava9_WhenStartDateAsTodayAndEndDateAs10DaysAhead() {
+        LocalDate start = LocalDate.now();
+        LocalDate end = start.plus(10L, ChronoUnit.DAYS);
+
+        RangeDatesIteration iteration = new RangeDatesIteration();
+
+        iteration.iterateBetweenDatesJava9(start, end);
+    }
+
+    @Test
+    public void givenIterateBetweenDatesJava8_WhenStartDateAsTodayAndEndDateAs10DaysAhead() {
+        LocalDate start = LocalDate.now();
+        LocalDate end = start.plus(10L, ChronoUnit.DAYS);
+
+        RangeDatesIteration iteration = new RangeDatesIteration();
+
+        iteration.iterateBetweenDatesJava8(start, end);
+    }
+
+    @Test
+    public void givenIterateBetweenDatesJava7_WhenStartDateAsTodayAndEndDateAs10DaysAhead() {
+        Calendar today = Calendar.getInstance();
+        Calendar calendar = Calendar.getInstance();
+        calendar.clear();
+        calendar.set(today.get(Calendar.YEAR), today.get(Calendar.MONTH), today.get(Calendar.DATE));
+        Date start = calendar.getTime();
+
+        calendar.add(Calendar.DATE, 10);
+        Date end = calendar.getTime();
+
+        RangeDatesIteration iteration = new RangeDatesIteration();
+
+        iteration.iterateBetweenDatesJava7(start, end);
+    }
+
+}