/*******************************************************************************
* Copyright (c) 2002, 2013 Object Factory Inc.
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* which accompanies this distribution, and is available at
* http://www.eclipse.org/legal/epl-v10.html
*
* Contributors:
* Object Factory Inc. - Initial implementation
*******************************************************************************/
package org.eclipse.ant.internal.ui.dtd.util;
import java.lang.ref.SoftReference;
/**
* Factory maintains a free list and, with FactoryObject, serves as a basis for factories of all types. Factory should only be subclassed in singleton
* classes; for static factories, it may be instantiated as a static object.
*
* @author Bob Foster
*/
public class Factory {
/**
* Return the first object on the free list or null if none.
*/
public FactoryObject getFree() {
Head head = getHead();
FactoryObject obj = head.next;
if (obj != null) {
head.next = obj.next();
obj.next(null);
}
return obj;
}
/**
* Add an object to the free list.
*/
public void setFree(FactoryObject obj) {
Head head = getHead();
obj.next(head.next);
head.next = obj;
}
private Head getHead() {
Head head = free.get();
if (head == null) {
// head is needed because you can't change
// the referent of a SoftReference.
// Without head, we would need to create
// a new SoftReference each time we remove
// a map from the list. With head, getting
// a free object only causes memory allocation
// when the list has been previously collected.
head = new Head();
free = new SoftReference<>(head);
}
return head;
}
private static class Head {
public FactoryObject next;
}
private SoftReference<Head> free = new SoftReference<>(new Head());
}