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// Copyright (C) 2002-2003 Jon A. Maxwell (JAM)
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
//
// This library 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. See the GNU
// Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
package net.sourceforge.jnlp.util;
import java.lang.ref.*;
import java.util.*;
/**
* This list stores objects automatically using weak references.
* Objects are added and removed from the list as normal, but may
* turn to null at any point (ie, indexOf(x) followed by get(x)
* may return null). The weak references are only removed when
* the trimToSize method is called so that the indices remain
* constant otherwise.<p>
*
* @author <a href="mailto:jmaxwell@users.sourceforge.net">Jon A. Maxwell (JAM)</a> - initial author
* @version $Revision: 1.3 $
*/
public class WeakList<E> extends AbstractList<E> {
/* list of weak references */
private ArrayList<WeakReference<E>> refs = new ArrayList<WeakReference<E>>();
/**
* Create a weak random-access list.
*/
public WeakList() {
}
/**
* Extract the hard reference out of a weak reference.
*/
private E deref(WeakReference<E> o) {
if (o != null)
return o.get();
else
return null;
}
/**
* Returns the object at the specified index, or null if the
* object has been collected.
*/
public E get(int index) {
return deref(refs.get(index));
}
/**
* Returns the size of the list, including already collected
* objects.
*/
public int size() {
return refs.size();
}
/**
* Sets the object at the specified position and returns the
* previous object at that position or null if it was already
* collected.
*/
public E set(int index, E element) {
return deref(refs.set(index, new WeakReference<E>(element)));
}
/**
* Inserts the object at the specified position in the list.
* Automatically creates a weak reference to the object.
*/
public void add(int index, E element) {
refs.add(index, new WeakReference<E>(element));
}
/**
* Removes the object at the specified position and returns it
* or returns null if it was already collected.
*/
public E remove(int index) {
return deref(refs.remove(index));
}
/**
* Returns a list of hard references to the objects. The
* returned list does not include the collected elements, so its
* indices do not necessarily correlate with those of this list.
*/
public List<E> hardList() {
List<E> result = new ArrayList<E>();
for (int i = 0; i < size(); i++) {
E tmp = get(i);
if (tmp != null)
result.add(tmp);
}
return result;
}
/**
* Compacts the list by removing references to collected
* objects.
*/
public void trimToSize() {
for (int i = size(); i-- > 0;)
if (get(i) == null)
remove(i);
}
}
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