Refactor duplicate code.

src/main/java/org/apache/commons/lang3/time/DateUtils.java

@@ -165,7 +165,7 @@ public class DateUtils {
      */
     public static boolean isSameDay(final Date date1, final Date date2) {
         if (date1 == null || date2 == null) {
-            throw new IllegalArgumentException("The date must not be null");
+            throw nullDateIllegalArgumentException();
         }
         final Calendar cal1 = Calendar.getInstance();
         cal1.setTime(date1);
@@ -189,7 +189,7 @@ public class DateUtils {
      */
     public static boolean isSameDay(final Calendar cal1, final Calendar cal2) {
         if (cal1 == null || cal2 == null) {
-            throw new IllegalArgumentException("The date must not be null");
+            throw nullDateIllegalArgumentException();
         }
         return cal1.get(Calendar.ERA) == cal2.get(Calendar.ERA) &&
                 cal1.get(Calendar.YEAR) == cal2.get(Calendar.YEAR) &&
@@ -210,7 +210,7 @@ public class DateUtils {
      */
     public static boolean isSameInstant(final Date date1, final Date date2) {
         if (date1 == null || date2 == null) {
-            throw new IllegalArgumentException("The date must not be null");
+            throw nullDateIllegalArgumentException();
         }
         return date1.getTime() == date2.getTime();
     }
@@ -228,7 +228,7 @@ public class DateUtils {
      */
     public static boolean isSameInstant(final Calendar cal1, final Calendar cal2) {
         if (cal1 == null || cal2 == null) {
-            throw new IllegalArgumentException("The date must not be null");
+            throw nullDateIllegalArgumentException();
         }
         return cal1.getTime().getTime() == cal2.getTime().getTime();
     }
@@ -248,7 +248,7 @@ public class DateUtils {
      */
     public static boolean isSameLocalTime(final Calendar cal1, final Calendar cal2) {
         if (cal1 == null || cal2 == null) {
-            throw new IllegalArgumentException("The date must not be null");
+            throw nullDateIllegalArgumentException();
         }
         return cal1.get(Calendar.MILLISECOND) == cal2.get(Calendar.MILLISECOND) &&
                 cal1.get(Calendar.SECOND) == cal2.get(Calendar.SECOND) &&
@@ -741,13 +741,17 @@ public class DateUtils {
      */
     public static Calendar round(final Calendar date, final int field) {
         if (date == null) {
-            throw new IllegalArgumentException("The date must not be null");
+            throw nullDateIllegalArgumentException();
         }
         final Calendar rounded = (Calendar) date.clone();
         modify(rounded, field, ModifyType.ROUND);
         return rounded;
     }
 
+    private static IllegalArgumentException nullDateIllegalArgumentException() {
+        return new IllegalArgumentException("The date must not be null");
+    }
+
     /**
      * <p>Rounds a date, leaving the field specified as the most
      * significant field.</p>
@@ -778,7 +782,7 @@ public class DateUtils {
      */
     public static Date round(final Object date, final int field) {
         if (date == null) {
-            throw new IllegalArgumentException("The date must not be null");
+            throw nullDateIllegalArgumentException();
         }
         if (date instanceof Date) {
             return round((Date) date, field);
@@ -830,7 +834,7 @@ public class DateUtils {
      */
     public static Calendar truncate(final Calendar date, final int field) {
         if (date == null) {
-            throw new IllegalArgumentException("The date must not be null");
+            throw nullDateIllegalArgumentException();
         }
         final Calendar truncated = (Calendar) date.clone();
         modify(truncated, field, ModifyType.TRUNCATE);
@@ -855,7 +859,7 @@ public class DateUtils {
      */
     public static Date truncate(final Object date, final int field) {
         if (date == null) {
-            throw new IllegalArgumentException("The date must not be null");
+            throw nullDateIllegalArgumentException();
         }
         if (date instanceof Date) {
             return truncate((Date) date, field);
@@ -909,7 +913,7 @@ public class DateUtils {
      */
     public static Calendar ceiling(final Calendar date, final int field) {
         if (date == null) {
-            throw new IllegalArgumentException("The date must not be null");
+            throw nullDateIllegalArgumentException();
         }
         final Calendar ceiled = (Calendar) date.clone();
         modify(ceiled, field, ModifyType.CEILING);
@@ -935,7 +939,7 @@ public class DateUtils {
      */
     public static Date ceiling(final Object date, final int field) {
         if (date == null) {
-            throw new IllegalArgumentException("The date must not be null");
+            throw nullDateIllegalArgumentException();
         }
         if (date instanceof Date) {
             return ceiling((Date) date, field);
@@ -1153,7 +1157,7 @@ public class DateUtils {
      */
     public static Iterator<Calendar> iterator(final Calendar focus, final int rangeStyle) {
         if (focus == null) {
-            throw new IllegalArgumentException("The date must not be null");
+            throw nullDateIllegalArgumentException();
         }
         Calendar start = null;
         Calendar end = null;
@@ -1243,7 +1247,7 @@ public class DateUtils {
      */
     public static Iterator<?> iterator(final Object focus, final int rangeStyle) {
         if (focus == null) {
-            throw new IllegalArgumentException("The date must not be null");
+            throw nullDateIllegalArgumentException();
         }
         if (focus instanceof Date) {
             return iterator((Date) focus, rangeStyle);
@@ -1663,7 +1667,7 @@ public class DateUtils {
      */
     private static long getFragment(final Calendar calendar, final int fragment, final TimeUnit unit) {
         if (calendar == null) {
-            throw  new IllegalArgumentException("The date must not be null");
+            throw  nullDateIllegalArgumentException();
         }
 
         long result = 0;