| /******************************************************************************* |
| * Copyright (c) 2002, 2013 Object Factory Inc. |
| * |
| * This program and the accompanying materials |
| * are made available under the terms of the Eclipse Public License 2.0 |
| * which accompanies this distribution, and is available at |
| * https://www.eclipse.org/legal/epl-2.0/ |
| * |
| * SPDX-License-Identifier: EPL-2.0 |
| * |
| * 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()); |
| } |
