BAEL-6397: Adding One Month to Current Date in Java (#14261)

core-java-modules/core-java-date-operations-3/pom.xml

@@ -13,4 +13,22 @@
         <version>0.0.1-SNAPSHOT</version>
     </parent>
     
+    <dependencies>
+        <dependency>
+            <groupId>joda-time</groupId>
+            <artifactId>joda-time</artifactId>
+            <version>${joda-time.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-lang3</artifactId>
+            <version>${commons-lang3.version}</version>
+        </dependency>
+    </dependencies>
+    
+    <properties>
+        <joda-time.version>2.12.5</joda-time.version>
+        <commons-lang3.version>3.12.0</commons-lang3.version>
+    </properties>
+
 </project>

core-java-modules/core-java-date-operations-3/src/test/java/com/baeldung/date/AddOneMonthToCurrentDateUnitTest.java

@@ -0,0 +1,79 @@
+package com.baeldung.date;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.time.LocalDate;
+import java.util.Calendar;
+import java.util.Date;
+import java.util.GregorianCalendar;
+
+import org.apache.commons.lang3.time.DateUtils;
+import org.junit.jupiter.api.Test;
+
+class AddOneMonthToCurrentDateUnitTest {
+
+    @Test
+    void givenCalendarDate_whenAddingOneMonth_thenDateIsChangedCorrectly() {
+        Calendar calendar = Calendar.getInstance();
+        // Dummy current date
+        calendar.set(2023, Calendar.APRIL, 20);
+
+        // add one month
+        calendar.add(Calendar.MONTH, 1);
+
+        assertEquals(Calendar.MAY, calendar.get(Calendar.MONTH));
+        assertEquals(20, calendar.get(Calendar.DAY_OF_MONTH));
+        assertEquals(2023, calendar.get(Calendar.YEAR));
+    }
+
+    @SuppressWarnings("deprecation")
+    @Test
+    void givenDate_whenAddingOneMonth_thenDateIsChangedCorrectly() {
+        // Dummy current date
+        Date currentDate = new Date(2023, Calendar.DECEMBER, 20);
+        // Expected Date
+        Date expectedDate = new Date(2024, Calendar.JANUARY, 20);
+
+        // add one month
+        currentDate.setMonth(currentDate.getMonth() + 1);
+
+        assertEquals(expectedDate, currentDate);
+    }
+
+    @Test
+    void givenJavaLocalDate_whenAddingOneMonth_thenDateIsChangedCorrectly() {
+        // Dummy current date
+        LocalDate localDate = LocalDate.of(2023, 12, 20);
+
+        // add one month
+        localDate = localDate.plusMonths(1);
+
+        assertEquals(1, localDate.getMonthValue());
+        assertEquals(20, localDate.getDayOfMonth());
+        assertEquals(2024, localDate.getYear());
+    }
+
+    @Test
+    void givenJodaTimeLocalDate_whenAddingOneMonth_thenDateIsChangedCorrectly() {
+        // Dummy current date
+        org.joda.time.LocalDate localDate = new org.joda.time.LocalDate(2023, 12, 20);
+
+        // add one month
+        localDate = localDate.plusMonths(1);
+
+        assertEquals(1, localDate.getMonthOfYear());
+        assertEquals(20, localDate.getDayOfMonth());
+        assertEquals(2024, localDate.getYear());
+    }
+
+    @Test
+    void givenApacheCommonsLangDateUtils_whenAddingOneMonth_thenDateIsChangedCorrectly() {
+        // Dummy current date
+        Date currentDate = new GregorianCalendar(2023, Calendar.APRIL, 20, 4, 0).getTime();
+        // Expected Date
+        Date expectedDate = new GregorianCalendar(2023, Calendar.MAY, 20, 4, 0).getTime();
+
+        assertEquals(expectedDate, DateUtils.addMonths(currentDate, 1));
+    }
+
+}