com.mchange.util.impl.CircularList Maven / Gradle / Ivy
/*
* Distributed as part of mchange-commons-java 0.2.11
*
* Copyright (C) 2015 Machinery For Change, Inc.
*
* Author: Steve Waldman
*
* This library is free software; you can redistribute it and/or modify
* it under the terms of EITHER:
*
* 1) The GNU Lesser General Public License (LGPL), version 2.1, as
* published by the Free Software Foundation
*
* OR
*
* 2) The Eclipse Public License (EPL), version 1.0
*
* You may choose which license to accept if you wish to redistribute
* or modify this work. You may offer derivatives of this work
* under the license you have chosen, or you may provide the same
* choice of license which you have been offered here.
*
* This software is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
*
* You should have received copies of both LGPL v2.1 and EPL v1.0
* along with this software; see the files LICENSE-EPL and LICENSE-LGPL.
* If not, the text of these licenses are currently available at
*
* LGPL v2.1: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html
* EPL v1.0: http://www.eclipse.org/org/documents/epl-v10.php
*
*/
/*
* This class modified from swaldman.util.CircularList,
* originally written by Steve Waldman at the MIT Media Lab
*/
package com.mchange.util.impl;
import java.util.*;
import com.mchange.util.*;
/**
* CircularList is a list class. Objects can be added
* at the beginning or end; they may be enumerated through
* forwards or backwards; they may be retrieved directly or
* by index from the front or rear. CircularLists can also
* be enumerated endlessly. If the list contains any elements at
* all, an "unterminated" Enumeration will always claim to have
* more elements... when it's done enumerating, it will start
* over again. The default Enumeration is of the usual,
* terminated variety, however.
*
* This class is a completely UNSYNCHRONIZED implementation
* class. Synchronize on calls where necessary.
*
*/
public class CircularList extends Object implements Cloneable
{
CircularListRecord firstRecord;
int size;
public CircularList()
{
this.firstRecord = null;
this.size = 0;
}
private void addElement(Object object, boolean first)
{
if (firstRecord == null)
firstRecord = new CircularListRecord(object);
else
{
CircularListRecord newRecord = new CircularListRecord(object, firstRecord.prev, firstRecord);
firstRecord.prev.next = newRecord;
firstRecord.prev = newRecord;
if (first) firstRecord = newRecord;
}
++size;
}
private void removeElement(boolean first)
{
if (size == 1)
firstRecord = null;
else
{
if (first) firstRecord = firstRecord.next;
zap(firstRecord.prev);
}
--size;
}
private void zap(CircularListRecord record)
{
record.next.prev = record.prev;
record.prev.next = record.next;
}
public void appendElement(Object object)
{addElement(object, false);}
public void addElementToFront(Object object)
{addElement(object, true);}
public void removeFirstElement()
{removeElement(true);}
public void removeLastElement()
{removeElement(false);}
public void removeFromFront(int count)
{
if (count > size)
throw new IndexOutOfBoundsException(count + ">" + size);
else for(int i = 0; i < count; ++i) removeElement(true);
}
public void removeFromBack(int count)
{
if (count > size)
throw new IndexOutOfBoundsException(count + ">" + size);
else for(int i = 0; i < count; ++i) removeElement(false);
}
public void removeAllElements()
{
size = 0;
firstRecord = null;
}
public Object getElementFromFront(int index)
{
if (index >= size)
throw new IndexOutOfBoundsException(index + ">=" + size);
else
{
CircularListRecord finger = firstRecord;
for (int i = 0; i < index; ++i)
finger = finger.next;
return finger.object;
}
}
public Object getElementFromBack(int index)
{
if (index >= size)
throw new IndexOutOfBoundsException(index + ">=" + size);
else
{
CircularListRecord finger = firstRecord.prev;
for (int i = 0; i < index; ++i)
finger = finger.prev;
return finger.object;
}
}
public Object getFirstElement()
{
try {return firstRecord.object;}
catch (NullPointerException e)
{throw new IndexOutOfBoundsException("CircularList is empty.");}
}
public Object getLastElement()
{
try {return firstRecord.prev.object;}
catch (NullPointerException e)
{throw new IndexOutOfBoundsException("CircularList is empty.");}
}
public Enumeration elements(boolean forward, boolean terminated)
{return new CircularListEnumeration(this, forward, terminated);}
public Enumeration elements(boolean forward)
{return elements(forward, true);}
public Enumeration elements()
{return elements(true, true);}
public int size()
{return size;}
/**
* Returns a shallow copy. The list is
* cloned, but not the elements within it.
*/
public Object clone()
{
//this could be much more effeicient...
CircularList out = new CircularList();
int len = this.size();
for (int i = 0; i < len; ++i)
out.appendElement(this.getElementFromFront(i));
return out;
}
public static void main(String[] argv)
{
CircularList list = new CircularList();
list.appendElement("Hello");
list.appendElement("There");
list.appendElement("Joe.");
for (Enumeration e = list.elements(); e.hasMoreElements();)
System.out.println("x " + e.nextElement());
}
}
class CircularListEnumeration extends Object implements Enumeration
{
boolean forward;
boolean terminated;
boolean done;
CircularListRecord startRecord;
CircularListRecord lastRecord;
CircularListEnumeration(CircularList list, boolean forward, boolean terminated)
{
if (list.firstRecord == null)
this.done = true;
else
{
this.done = false;
this.forward = forward;
this.terminated = terminated;
this.startRecord = (forward ? list.firstRecord : list.firstRecord.prev);
this.lastRecord = (forward ? startRecord.prev : startRecord);
}
}
public boolean hasMoreElements()
{return !done;}
public Object nextElement()
{
if (done)
throw new NoSuchElementException();
else
{
lastRecord = (forward ? lastRecord.next : lastRecord.prev);
if (terminated && lastRecord == (forward ? startRecord.prev : startRecord))
done = true;
return lastRecord.object;
}
}
}
class CircularListRecord
{
Object object;
CircularListRecord next;
CircularListRecord prev;
CircularListRecord(Object object, CircularListRecord prev, CircularListRecord next)
{
this.object = object;
this.prev = prev;
this.next = next;
}
CircularListRecord(Object object) //for first record
{
this.object = object;
this.prev = this;
this.next = this;
}
}