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The Apache Commons Codec package contains simple encoder and decoders for various formats such as Base64 and Hexadecimal. In addition to these widely used encoders and decoders, the codec package also maintains a collection of phonetic encoding utilities.
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/*
* Copyright (c) 2005, Graph Builder
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* * Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
*
* * 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.
*
* * Neither the name of Graph Builder 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.
*/

package com.graphbuilder.struc;

public class LinkedList {

	protected Node head = null;
	protected Node tail = null;
	protected int size = 0;

	public LinkedList() {}

	public static class Node {
		protected LinkedList list = null;
		protected Node next = null;
		protected Node prev = null;
		protected Object userObject = null;

		protected Node(LinkedList list, Object userObject) {
			this.list = list;
			this.userObject = userObject;
		}

		public LinkedList list() {
			return list;
		}

		public Node next() {
			return next;
		}

		public Node prev() {
			return prev;
		}

		public Object getUserObject() {
			return userObject;
		}

		public void setUserObject(Object userObject) {
			this.userObject = userObject;
		}

		public void insertBefore(Object o) {
			list.insertBefore(this, o);
		}

		public void insertAfter(Object o) {
			list.insertAfter(this, o);
		}

		public void remove() {
			list.removeNode(this);
		}
	}

	protected Node createNode(Object o) {
		return new Node(this, o);
	}

	protected void insertBefore(Node n, Object o) {
		Node p = createNode(o);

		if (size == 0) {
			head = p;
			tail = p;
		}
		else {
			if (n == head) {
				p.next = head;
				head.prev = p;
				head = p;
			}
			else {
				n.prev.next = p;
				p.prev = n.prev;
				n.prev = p;
				p.next = n;
			}
		}

		size++;
	}

	protected void insertAfter(Node n, Object o) {
		Node p = createNode(o);

		if (size == 0) {
			head = p;
			tail = p;
		}
		else {
			if (n == tail) {
				p.prev = tail;
				tail.next = p;
				tail = p;
			}
			else {
				n.next.prev = p;
				p.next = n.next;
				n.next = p;
				p.prev = n;
			}
		}

		size++;
	}

	protected Object removeNode(Node n) {
		if (size == 0)
			return null;

		Object o = n.userObject;

		if (n == head) {
			head = head.next;

			if (head == null)
				tail = null;
			else
				head.prev = null;
		}
		else if (n == tail) {
			tail = tail.prev;
			tail.next = null;
		}
		else {
			n.prev.next = n.next;
			n.next.prev = n.prev;
		}

		n.list = null;
		size--;
		return o;
	}

	public Node getHead() {
		return head;
	}

	public Node getTail() {
		return tail;
	}

	public void addToHead(Object o) {
		insertBefore(head, o);
	}

	public void addToTail(Object o) {
		insertAfter(tail, o);
	}

	public Object removeHead() {
		return removeNode(head);
	}

	public Object removeTail() {
		return removeNode(tail);
	}

	public int size() {
		return size;
	}

	public boolean isEmpty() {
		return size == 0;
	}

	public String toString() {
		StringBuffer sb = new StringBuffer(6 * size);
		sb.append("[");
		Node n = head;

		if (n != null) {
			sb.append(n.userObject);
			n = n.next;
		}

		while (n != null) {
			sb.append(", ");
			sb.append(n.userObject);
			n = n.next;
		}

		return sb.append("]").toString();
	}
}