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+/* -*- Mode: Java; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * This file is part of the LibreOffice project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ *
+ * This file incorporates work covered by the following license notice:
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed
+ * with this work for additional information regarding copyright
+ * ownership. The ASF licenses this file to you under the Apache
+ * License, Version 2.0 (the "License"); you may not use this file
+ * except in compliance with the License. You may obtain a copy of
+ * the License at http://www.apache.org/licenses/LICENSE-2.0 .
+ */
+
+package com.sun.star.uno;
+
+/**
+ * This class holds weak reference to an object.
+ *
+ * <p>It actually holds a reference to a <code>com.sun.star.XAdapter</code>
+ * implementation and obtains a hard reference if necessary.
+ */
+public class WeakReference
+{
+ private OWeakRefListener m_listener;
+ // There is no default constructor. Every instance must register itself with the
+ // XAdapter interface, which is done in the constructors. Assume we have this code
+ // WeakReference ref= new WeakReference();
+ // ref = someOtherWeakReference;
+ //
+ // ref would not be notified (XReference.dispose()) because it did not register
+ // itself. Therefore the XAdapter would be kept alive although this is not
+ // necessary.
+
+ /**
+ * Creates an instance of this class.
+ *
+ * @param obj another instance that is to be copied.
+ */
+ public WeakReference(WeakReference obj)
+ {
+ if (obj == null) {
+ return;
+ }
+ Object weakImpl = obj.get();
+ if (weakImpl == null) {
+ return;
+ }
+ XWeak weak = UnoRuntime.queryInterface(XWeak.class, weakImpl);
+ if (weak != null) {
+ XAdapter adapter = weak.queryAdapter();
+ if (adapter != null)
+ m_listener = new OWeakRefListener(adapter);
+ }
+ }
+
+ /**
+ * Creates an instance of this class.
+ *
+ * @param obj XWeak implementation.
+ */
+ public WeakReference(Object obj)
+ {
+ XWeak weak= UnoRuntime.queryInterface(XWeak.class, obj);
+ if (weak != null)
+ {
+ XAdapter adapter= weak.queryAdapter();
+ if (adapter != null)
+ m_listener= new OWeakRefListener(adapter);
+ }
+ }
+
+ /**
+ * Returns a hard reference to the object that is kept weak by this class.
+ *
+ * @return a hard reference to the XWeak implementation.
+ */
+ public Object get()
+ {
+ if (m_listener != null)
+ return m_listener.get();
+ return null;
+ }
+}
+
+/**
+ * Implementation of com.sun.star.uno.XReference for use with WeakReference.
+ *
+ * <p>It keeps the XAdapter implementation and registers always with it.
+ * Deregistering occurs on notification by the adapter and the adapter is
+ * released.</p>
+ */
+class OWeakRefListener implements XReference
+{
+ private XAdapter m_adapter;
+
+ /**
+ * The constructor registered this object with adapter.
+ *
+ * @param adapter the XAdapter implementation.
+ */
+ OWeakRefListener( XAdapter adapter)
+ {
+ m_adapter= adapter;
+ m_adapter.addReference(this);
+ }
+
+ /**
+ * Method of <code>com.sun.star.uno.XReference</code>.
+ *
+ * <p>When called, it deregisters this object with the adapter and releases
+ * the reference to it.</p>
+ */
+ synchronized public void dispose()
+ {
+ if (m_adapter != null)
+ {
+ m_adapter.removeReference(this);
+ m_adapter= null;
+ }
+ }
+
+ /**
+ * Obtains a hard reference to the object which is kept weak by the adapter
+ * and returns it.
+ *
+ * @return hard reference to the otherwise weakly kept object.
+ */
+ synchronized Object get()
+ {
+ Object retVal= null;
+ if (m_adapter != null)
+ {
+ retVal= m_adapter.queryAdapted();
+ if (retVal == null)
+ {
+ // If this object registered as listener with XAdapter while it was notifying
+ // the listeners then this object might not have been notified. If queryAdapted
+ // returned null then the weak kept object is dead and the listeners have already
+ // been notified. And we missed it.
+ m_adapter.removeReference(this);
+ m_adapter= null;
+ }
+ }
+ return retVal;
+ }
+}
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */