Glassfish example source code file (DoubleLinkedList.java)

This example Glassfish source code file (DoubleLinkedList.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Glassfish tags/keywords

clear, clear, doublelinkedlist, fixup, fixup, if, insert, insert, linkable, linkable, no, point, set, yes

The Glassfish DoubleLinkedList.java source code

/*
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
 *
 * Copyright (c) 1997-2010 Oracle and/or its affiliates. All rights reserved.
 *
 * The contents of this file are subject to the terms of either the GNU
 * General Public License Version 2 only ("GPL") or the Common Development
 * and Distribution License("CDDL") (collectively, the "License").  You
 * may not use this file except in compliance with the License.  You can
 * obtain a copy of the License at
 * https://glassfish.dev.java.net/public/CDDL+GPL_1_1.html
 * or packager/legal/LICENSE.txt.  See the License for the specific
 * language governing permissions and limitations under the License.
 *
 * When distributing the software, include this License Header Notice in each
 * file and include the License file at packager/legal/LICENSE.txt.
 *
 * GPL Classpath Exception:
 * Oracle designates this particular file as subject to the "Classpath"
 * exception as provided by Oracle in the GPL Version 2 section of the License
 * file that accompanied this code.
 *
 * Modifications:
 * If applicable, add the following below the License Header, with the fields
 * enclosed by brackets [] replaced by your own identifying information:
 * "Portions Copyright [year] [name of copyright owner]"
 *
 * Contributor(s):
 * If you wish your version of this file to be governed by only the CDDL or
 * only the GPL Version 2, indicate your decision by adding "[Contributor]
 * elects to include this software in this distribution under the [CDDL or GPL
 * Version 2] license."  If you don't indicate a single choice of license, a
 * recipient has the option to distribute your version of this file under
 * either the CDDL, the GPL Version 2 or to extend the choice of license to
 * its licensees as provided above.  However, if you add GPL Version 2 code
 * and therefore, elected the GPL Version 2 license, then the option applies
 * only if the new code is made subject to such option by the copyright
 * holder.
 */

/*
 * ConnectionImpl.java
 *
 * Create on March 3, 2000
 */

package com.sun.jdo.spi.persistence.utility;

/**
 * This class defines a thread-safe double linked-list.
 * The list is usable by any class that implements the
 * com.forte.util.Linkable interface.  This class allows
 * a linkable object it be inserted or removed from anywhere
 * in the list.
 *
 * RESTRICTION: An object can only be a member of 1 list
 * at a time.
 */
public class DoubleLinkedList
{

	// Instance variables.

	/**
	 * Head of linked list.
	 */
	public Linkable						head;

	/**
	 * Tail of linked list.
	 */
	public Linkable						tail;

	/**
	 * Size of linked list.
	 */
	public int							size;

	/**
	 * Default constructor.
	 */
	public DoubleLinkedList()
	{
		this.head = null;
		this.size = 0;
		this.tail = null;
	}


	// Public Methods.

	/**
	 * Return the object at the head of a linked list.
	 *
	 */
	public synchronized Linkable getHead()
	{
		return this.head;
	}

	/**
	 * Return the object at the tail of a linked list.
	 *
	 */
	public synchronized Linkable getTail()
	{
		return this.tail;
	}


	/**
	 * Return size of the linked list.
	 *
	 */
	public synchronized int getSize()
	{
		return this.size;
	}


	/**
	 * Insert an object at the head of a linked list.
	 *
	 */
	public synchronized void insertAtHead(Linkable node)
	{
		if (node instanceof Linkable)
		{
			if (this.head == null)
			{
				node.setNext(null);				// Fixup node nextlink.
				node.setPrevious(null);			// Fixup node backlink.
				this.head = node;				// Insert node at head of list.
			}
			else
			{
				Linkable oldHead = this.head;	// Fixup current head node.
				oldHead.setPrevious(node);		// Set backlink to new node.
				node.setNext(oldHead);			// Fixup new node nextlink.
				node.setPrevious(null);			// Fixup new node backlink.
				this.head = node;				// Insert node at head of list.
			}
			if (this.tail == null)				// If list was empty,
			{
				this.tail = node;				// Insert node at tail of list.
			}
			this.size++;
		}
	}

	/**
	 * Insert an object at the tail of a linked list.
	 *
	 */
	public synchronized void insertAtTail(Linkable node)
	{
		if (node instanceof Linkable)
		{
			if (this.tail == null)
			{
				node.setNext(null);				// Fixup node nextlink.
				node.setPrevious(null);			// Fixup node backlink.
				this.tail = node;				// Insert node at end of list.
			}
			else
			{
				Linkable oldTail = this.tail;	// Fixup current tail node.
				oldTail.setNext(node);			// Set backlink to new node.
				node.setNext(null) ;			// Fixup new node backlink.
				node.setPrevious(oldTail);		// Fixup new node nextlink.
				this.tail = node;				// Insert node at end of list.
			}
			if (this.head == null)				// If list was empty,
			{
				this.head = node;				// Insert node at head of list.
			}
			this.size++;
		}
	}



	/**
	 * Remove and return an object from the head of a linked list.
	 *
	 */
	public synchronized Linkable removeFromHead()
	{
		Linkable node = this.head;
		if (node instanceof Linkable)
		{
			this.head = node.getNext();	// Set head to next node.
			if (this.head == null)		// If we emptied the list,
			{
				this.tail = null;		// Fixup the tail pointer.
			}
			else
			{
				this.head.setPrevious(null);// Clear head node backlink.
			}
			node.setNext(null);			// Clear removed node nextlink.
			node.setPrevious(null);		// Clear romoved node backlink.
			this.size--;
		}
		return node;
	}

	/**
	 * Remove and return an object from the tail of a linked list.
	 *
	 */
	public synchronized Linkable removeFromTail()
	{
		Linkable node = this.tail;
		if (node instanceof Linkable)
		{
			this.tail = node.getPrevious();	// Set tail to previous node.
			if (this.tail == null)			// If we emptied the list,
			{
				this.head = null;			// Fixup the head pointer.
			}
			else
			{
				this.tail.setNext(null);	// Clear tail node nextlink.
			}
			node.setNext(null);				// Clear removed node nextlink.
			node.setPrevious(null);			// Clear removed node backlink.
			this.size--;
		}
		return node;
	}

	/**
	 * Remove the specified object from anywhere in the linked list.
	 * This method is usually used by the object to remove itself
	 * from the list.
	 *
	 */
	public synchronized void removeFromList(Linkable node)
	{
		if ((this.size <= 0) || ((this.head == null) && (this.tail == null)))
		{
			return;
		} 
		if (node instanceof Linkable)
		{
			Linkable p = node.getPrevious();	// Reference to previous node.
			Linkable n = node.getNext();		// Reference to next node. 

			if (p == null)			// Is this the first (or only) node in the list?
			{
				this.head = n;		// Yes, set the head of the list to point to the next.
			}
			else
			{
				p.setNext(n);		// No, set the previous node to point to the next.
			}

			if (n == null)			// Is this the last (or only) node in the list?
			{
				this.tail = p;		// Yes, set the tail to point to the previous.
			}
			else
			{
				n.setPrevious(p);	// No, set the next node to point to the previous.
			}

			node.setNext(null);
			node.setPrevious(null);
			this.size--;
		}
	}


	/**
	 * Insert an object anywhere into the linked list.
	 *
	 * @param afternode			the new node will be inserted after this node
	 * @param newnode			the new node to be inserted
	 */
	public synchronized void insertIntoList(Linkable afternode, Linkable newnode)
	{
		if ((newnode instanceof Linkable) && (afternode instanceof Linkable))
		{
			if (this.tail == afternode)			// If inserting at the tail,
			{
				this.insertAtTail(newnode);		// Use insertAtTail method.
			}
			else
			{
				Linkable nextnode = afternode.getNext();
				newnode.setNext(nextnode);		// Point to next node.
				newnode.setPrevious(afternode);	// Point to previous node.
				afternode.setNext(newnode);		// Fixup backlink in afternode.
				nextnode.setPrevious(newnode);	// Fixup nextlink in next node.
			}
			this.size++;
		}
	}

	/**
	 * Return a string representation of this DoubleLinkedList object.
	 * <p> 
	 * @return  String representation of this object.
	 */
	public synchronized String toString()
	{
		/*		boolean dif = ThreadContext.lgr().test
			(	// Check for trace flag sp:1:1
				TraceLogger.CONFIGURATION,
				TraceLogger.SVC_SP,
				SPLogFlags.CFG_DIFFABLE_EXCEPTS,
				1
			);
		String buf = "DoubleLinkedList@\n";
		if(!dif)
		{
			buf = buf + "      head = " + this.head + "\n";
			buf = buf + "      tail = " + this.tail + "\n";
		}
		buf = buf + "      size = " + this.size + "\n";
        return buf;
		*/

		return null;
    }
}