diff -r 000000000000 -r fb9019fb1bf7 src/net/fortuna/ical4j/model/NumberList.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/net/fortuna/ical4j/model/NumberList.java	Tue Feb 10 18:12:00 2015 +0100
@@ -0,0 +1,154 @@
+/**
+ * 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.ArrayList;
+import java.util.Iterator;
+import java.util.StringTokenizer;
+
+import net.fortuna.ical4j.util.Numbers;
+
+/**
+ * $Id$ [29-May-2004]
+ *
+ * Defines a list of numbers.
+ * 
+ * @author Ben Fortuna
+ */
+public class NumberList extends ArrayList implements Serializable {
+    
+    private static final long serialVersionUID = -1667481795613729889L;
+
+    private final int minValue;
+    
+    private final int maxValue;
+
+    private final boolean allowsNegativeValues;
+    
+    /**
+     * Default constructor.
+     */
+    public NumberList() {
+    	this(Integer.MIN_VALUE, Integer.MAX_VALUE, true);
+    }
+
+    /**
+     * Constructor with limits.
+     * @param minValue the minimum allowable value
+     * @param maxValue the maximum allowable value
+     * @param allowsNegativeValues indicates whether negative values are allowed
+     */
+    public NumberList(int minValue, int maxValue, boolean allowsNegativeValues) {
+    	this.minValue = minValue;
+    	this.maxValue = maxValue;
+        this.allowsNegativeValues = allowsNegativeValues;
+    }
+
+    /**
+     * Constructor.
+     * @param aString a string representation of a number list
+     */
+    public NumberList(final String aString) {
+    	this(aString, Integer.MIN_VALUE, Integer.MAX_VALUE, true);
+    }
+    
+    /**
+     * @param aString a string representation of a number list
+     * @param minValue the minimum allowable value
+     * @param maxValue the maximum allowable value
+     * @param allowsNegativeValues indicates whether negative values are allowed
+     */
+    public NumberList(final String aString, int minValue, int maxValue, boolean allowsNegativeValues) {
+    	this(minValue, maxValue, allowsNegativeValues);
+        final StringTokenizer t = new StringTokenizer(aString, ",");
+        while (t.hasMoreTokens()) {
+        	final int value = Numbers.parseInt(t.nextToken());
+            add(new Integer(value));
+        }
+    }
+
+    /**
+     * @param aNumber a number to add to the list
+     * @return true if the number was added, otherwise false
+     */
+    public final boolean add(final Integer aNumber) {
+        int abs = aNumber.intValue();
+        if ((abs >> 31 | -abs >>> 31) < 0) {
+            if (!allowsNegativeValues) {
+                throw new IllegalArgumentException("Negative value not allowed: " + aNumber);
+            }
+            abs = Math.abs(abs);
+        }
+    	if (abs < minValue || abs > maxValue) {
+    		throw new IllegalArgumentException(
+    		        "Value not in range [" + minValue + ".." + maxValue + "]: " + aNumber);
+    	}
+        return add((Object) aNumber);
+    }
+    
+    /**
+     * Overrides superclass to throw an <code>IllegalArgumentException</code>
+     * where argument is not a <code>java.lang.Integer</code>.
+     * @param arg0 an object to add
+     * @return true if the object was added, otherwise false
+     * @see List#add(E)
+     */
+    public final boolean add(final Object arg0) {
+        if (!(arg0 instanceof Integer)) {
+            throw new IllegalArgumentException("Argument not a " + Integer.class.getName());
+        }
+        return super.add(arg0);
+    }
+
+    /**
+     * @param aNumber a number to remove from the list
+     * @return true if the number was removed, otherwise false
+     */
+    public final boolean remove(final Integer aNumber) {
+        return remove((Object) aNumber);
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    public final String toString() {
+        final StringBuffer b = new StringBuffer();
+        for (final Iterator i = iterator(); i.hasNext();) {
+            b.append(i.next());
+            if (i.hasNext()) {
+                b.append(',');
+            }
+        }
+        return b.toString();
+    }
+}