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diff --git a/israfil-foundation-container/src/main/java/net/israfil/foundation/container/util/NonDuplicateStack.java b/israfil-foundation-container/src/main/java/net/israfil/foundation/container/util/NonDuplicateStack.java
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+++ b/israfil-foundation-container/src/main/java/net/israfil/foundation/container/util/NonDuplicateStack.java
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+/*
+ * Copyright (c) 2008 Israfil Consulting Services Corporation
+ * Copyright (c) 2008 Christian Edward Gruber
+ * All Rights Reserved
+ * 
+ * This software is licensed under the Berkeley Standard Distribution license,
+ * (BSD license), as defined below:
+ * 
+ * Redistribution and use in source and binary forms, with or without 
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this 
+ *    list of conditions and the following disclaimer.
+ * 2. 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.
+ * 3. Neither the name of Israfil Consulting Services nor the names of its 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.
+ * 
+ * $Id: Copyright.java 618 2008-04-14 14:03:03Z christianedwardgruber $
+ */
+package net.israfil.foundation.container.util;
+
+import java.util.Stack;
+
+/**
+ * A simple stack object which throws an IllegalArgumentException if an 
+ * attempt is made to push an object already contained within the stack.
+ * 
+ * Primarily used for circular reference detection.
+ * 
+ * @author <a href="mailto:cgruber@israfil.net">Christian Edward Gruber </a>
+ */
+public class NonDuplicateStack<T> extends Stack<T> {
+
+	private static final long serialVersionUID = -5777711467165769847L;
+
+	public T push(T item) {
+		if (contains(item)) throw new IllegalArgumentException("Duplicate item.");
+		return super.push(item);
+	}
+	
+}