diff -r 000000000000 -r fb9019fb1bf7 src/net/fortuna/ical4j/model/WeekDay.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/net/fortuna/ical4j/model/WeekDay.java	Tue Feb 10 18:12:00 2015 +0100
@@ -0,0 +1,284 @@
+/**
+ * Copyright (c) 2012, Ben Fortuna
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ *  o Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ *  o Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution.
+ *
+ *  o Neither the name of Ben Fortuna nor the names of any other contributors
+ * may be used to endorse or promote products derived from this software
+ * without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+ * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+ * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+package net.fortuna.ical4j.model;
+
+import java.io.Serializable;
+import java.util.Calendar;
+
+import net.fortuna.ical4j.util.Numbers;
+
+import org.apache.commons.lang.ObjectUtils;
+import org.apache.commons.lang.builder.HashCodeBuilder;
+
+/**
+ * $Id$
+ * 
+ * Created: 19/12/2004
+ *
+ * Defines a day of the week with a possible offset related to
+ * a MONTHLY or YEARLY occurrence.
+ * 
+ * @author Ben Fortuna
+ */
+public class WeekDay implements Serializable {
+    
+    private static final long serialVersionUID = -4412000990022011469L;
+
+    /**
+     * Sunday.
+     */
+    public static final WeekDay SU = new WeekDay("SU", 0);
+
+    /**
+     * Monday.
+     */
+    public static final WeekDay MO = new WeekDay("MO", 0);
+
+    /**
+     * Tuesday.
+     */
+    public static final WeekDay TU = new WeekDay("TU", 0);
+
+    /**
+     * Wednesday.
+     */
+    public static final WeekDay WE = new WeekDay("WE", 0);
+
+    /**
+     * Thursday.
+     */
+    public static final WeekDay TH = new WeekDay("TH", 0);
+
+    /**
+     * Friday.
+     */
+    public static final WeekDay FR = new WeekDay("FR", 0);
+
+    /**
+     * Saturday.
+     */
+    public static final WeekDay SA = new WeekDay("SA", 0);
+
+    private String day;
+    
+    private int offset;
+    
+    /**
+     * @param value a string representation of a week day
+     */
+    public WeekDay(final String value) {
+        if (value.length() > 2) {
+            offset = Numbers.parseInt(value.substring(0, value.length() - 2));
+        }
+        else {
+            offset = 0;
+        }
+        day = value.substring(value.length() - 2);
+        validateDay();
+    }
+    
+    /**
+     * @param day a string representation of a week day
+     * @param offset a month offset value
+     */
+    private WeekDay(final String day, final int offset) {
+        this.day = day;
+        this.offset = offset;
+    }
+    
+    /**
+     * Constructs a new weekday instance based on the specified
+     * instance and offset.
+     * @param weekDay a week day template for the instance
+     * @param offset a month offset value
+     */
+    public WeekDay(final WeekDay weekDay, final int offset) {
+        this.day = weekDay.getDay();
+        this.offset = offset;
+    }
+    
+    private void validateDay() {
+        if (!SU.day.equals(day)
+            && !MO.day.equals(day)
+            && !TU.day.equals(day)
+            && !WE.day.equals(day)
+            && !TH.day.equals(day)
+            && !FR.day.equals(day)
+            && !SA.day.equals(day)) {
+            throw new IllegalArgumentException("Invalid day: " + day);
+        }
+    }
+    /**
+     * @return Returns the day.
+     */
+    public final String getDay() {
+        return day;
+    }
+    
+    /**
+     * @return Returns the offset.
+     */
+    public final int getOffset() {
+        return offset;
+    }
+        
+    /**
+     * {@inheritDoc}
+     */
+    public final String toString() {
+        final StringBuffer b = new StringBuffer();
+        if (getOffset() != 0) {
+            b.append(getOffset());
+        }
+        b.append(getDay());
+        return b.toString();
+    }
+    
+    /**
+     * Returns a weekday representation of the specified calendar.
+     * @param cal a calendar (java.util)
+     * @return a weekday instance representing the specified calendar
+     */
+    public static final WeekDay getWeekDay(final Calendar cal) {
+        return new WeekDay(getDay(cal.get(Calendar.DAY_OF_WEEK)), 0);
+    }
+    
+    /**
+     * Returns a weekday/offset representation of the specified calendar.
+     * @param cal a calendar (java.util)
+     * @return a weekday instance representing the specified calendar
+     */
+    public static final WeekDay getMonthlyOffset(final Calendar cal) {
+        return new WeekDay(getDay(cal.get(Calendar.DAY_OF_WEEK)), cal.get(Calendar.DAY_OF_WEEK_IN_MONTH));
+    }
+    
+    /**
+     * Returns a weekday/negative offset representation of the specified calendar.
+     * @param cal a calendar (java.util)
+     * @return a weekday instance representing the specified calendar
+     */
+    public static final WeekDay getNegativeMonthlyOffset(final Calendar cal) {
+        return new WeekDay(getDay(cal.get(Calendar.DAY_OF_WEEK)), cal.get(Calendar.DAY_OF_WEEK_IN_MONTH) - 6);
+    }
+    
+    /**
+     * Returns the corresponding day constant to the specified
+     * java.util.Calendar.DAY_OF_WEEK property.
+     * @param calDay a property value of java.util.Calendar.DAY_OF_WEEK
+     * @return a string, or null if an invalid DAY_OF_WEEK property is
+     * specified
+     */
+    public static WeekDay getDay(final int calDay) {
+        WeekDay day = null;
+        switch (calDay) {
+            case Calendar.SUNDAY:
+                day = SU;
+                break;
+            case Calendar.MONDAY:
+                day = MO;
+                break;
+            case Calendar.TUESDAY:
+                day = TU;
+                break;
+            case Calendar.WEDNESDAY:
+                day = WE;
+                break;
+            case Calendar.THURSDAY:
+                day = TH;
+                break;
+            case Calendar.FRIDAY:
+                day = FR;
+                break;
+            case Calendar.SATURDAY:
+                day = SA;
+                break;
+            default:
+                break;
+        }
+        return day;
+    }
+    
+    /**
+     * Returns the corresponding <code>java.util.Calendar.DAY_OF_WEEK</code>
+     * constant for the specified <code>WeekDay</code>.
+     * @param weekday a week day instance
+     * @return the corresponding <code>java.util.Calendar</code> day
+     */
+    public static int getCalendarDay(final WeekDay weekday) {
+        int calendarDay = -1;
+        if (SU.getDay().equals(weekday.getDay())) {
+            calendarDay = Calendar.SUNDAY;
+        }
+        else if (MO.getDay().equals(weekday.getDay())) {
+            calendarDay = Calendar.MONDAY;
+        }
+        else if (TU.getDay().equals(weekday.getDay())) {
+            calendarDay = Calendar.TUESDAY;
+        }
+        else if (WE.getDay().equals(weekday.getDay())) {
+            calendarDay = Calendar.WEDNESDAY;
+        }
+        else if (TH.getDay().equals(weekday.getDay())) {
+            calendarDay = Calendar.THURSDAY;
+        }
+        else if (FR.getDay().equals(weekday.getDay())) {
+            calendarDay = Calendar.FRIDAY;
+        }
+        else if (SA.getDay().equals(weekday.getDay())) {
+            calendarDay = Calendar.SATURDAY;
+        }
+        return calendarDay;
+    }
+    
+    /**
+     * {@inheritDoc}
+     */
+    public final boolean equals(final Object arg0) {
+        if (arg0 == null) {
+            return false;
+        }
+        if (!(arg0 instanceof WeekDay)) {
+            return false;
+        }
+        final WeekDay wd = (WeekDay) arg0;
+        return ObjectUtils.equals(wd.getDay(), getDay())
+            && wd.getOffset() == getOffset();
+    }
+    
+    /**
+     * {@inheritDoc}
+     */
+    public final int hashCode() {
+        return new HashCodeBuilder().append(getDay())
+            .append(getOffset()).toHashCode();
+    }
+}