BAEL-6597: How to get the last Day of the Month in Java (#14191)

azhwani · web-flow · commit 8e6bdc020597 · 2023-06-26T14:05:24.000+02:00
diff --git a/core-java-modules/core-java-date-operations-3/src/main/java/com/baeldung/lastdaymonth/LastDayOfMonth.java b/core-java-modules/core-java-date-operations-3/src/main/java/com/baeldung/lastdaymonth/LastDayOfMonth.java
@@ -0,0 +1,32 @@
+package com.baeldung.lastdaymonth;
+
+import java.time.LocalDate;
+import java.time.YearMonth;
+import java.time.temporal.TemporalAdjusters;
+import java.util.Calendar;
+
+public class LastDayOfMonth {
+
+    static int getLastDayOfMonthUsingCalendar(int month) {
+        Calendar cal = Calendar.getInstance();
+        cal.set(Calendar.MONTH, month);
+        return cal.getActualMaximum(Calendar.DAY_OF_MONTH);
+    }
+
+    static int getLastDayOfMonthUsingTemporalAdjusters(LocalDate date) {
+        return date.with(TemporalAdjusters.lastDayOfMonth())
+          .getDayOfMonth();
+    }
+
+    static int getLastDayOfMonthUsingYearMonth(YearMonth date) {
+        return date.atEndOfMonth()
+          .getDayOfMonth();
+    }
+
+    static int getLastDayOfMonthUsingJodaTime(org.joda.time.LocalDate date) {
+        return date.dayOfMonth()
+          .withMaximumValue()
+          .getDayOfMonth();
+    }
+
+}
diff --git a/core-java-modules/core-java-date-operations-3/src/test/java/com/baeldung/lastdaymonth/LastDayOfMonthUnitTest.java b/core-java-modules/core-java-date-operations-3/src/test/java/com/baeldung/lastdaymonth/LastDayOfMonthUnitTest.java
@@ -0,0 +1,40 @@
+package com.baeldung.lastdaymonth;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.time.LocalDate;
+import java.time.YearMonth;
+
+import org.junit.jupiter.api.Test;
+
+class LastDayOfMonthUnitTest {
+
+    @Test
+    void givenMonth_whenUsingCalendar_thenReturnLastDay() {
+        assertEquals(31, LastDayOfMonth.getLastDayOfMonthUsingCalendar(0));
+        assertEquals(30, LastDayOfMonth.getLastDayOfMonthUsingCalendar(3));
+        assertEquals(31, LastDayOfMonth.getLastDayOfMonthUsingCalendar(9));
+    }
+
+    @Test
+    void givenMonth_whenUsingTemporalAdjusters_thenReturnLastDay() {
+        assertEquals(31, LastDayOfMonth.getLastDayOfMonthUsingTemporalAdjusters(LocalDate.of(2023, 1, 1)));
+        assertEquals(30, LastDayOfMonth.getLastDayOfMonthUsingTemporalAdjusters(LocalDate.of(2023, 4, 1)));
+        assertEquals(31, LastDayOfMonth.getLastDayOfMonthUsingTemporalAdjusters(LocalDate.of(2023, 10, 1)));
+    }
+
+    @Test
+    void givenMonth_whenUsingYearMonth_thenReturnLastDay() {
+        assertEquals(31, LastDayOfMonth.getLastDayOfMonthUsingYearMonth(YearMonth.of(2023, 1)));
+        assertEquals(30, LastDayOfMonth.getLastDayOfMonthUsingYearMonth(YearMonth.of(2023, 4)));
+        assertEquals(31, LastDayOfMonth.getLastDayOfMonthUsingYearMonth(YearMonth.of(2023, 10)));
+    }
+
+    @Test
+    void givenMonth_whenUsingJodaTime_thenReturnLastDay() {
+        assertEquals(31, LastDayOfMonth.getLastDayOfMonthUsingJodaTime(org.joda.time.LocalDate.parse("2023-1-1")));
+        assertEquals(30, LastDayOfMonth.getLastDayOfMonthUsingJodaTime(org.joda.time.LocalDate.parse("2023-4-1")));
+        assertEquals(31, LastDayOfMonth.getLastDayOfMonthUsingJodaTime(org.joda.time.LocalDate.parse("2023-10-1")));
+    }
+
+}
