/* * Copyright (c) 2005, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation.  Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code 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 General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package com.sun.jmx.mbeanserver; import java.lang.ref.WeakReference;import java.util.WeakHashMap;import javax.management.Descriptor;import javax.management.ImmutableDescriptor;import javax.management.JMX; public class DescriptorCache {    private DescriptorCache() {    }     static DescriptorCache getInstance() {        return instance;    }     public static DescriptorCache getInstance(JMX proof) {        if (proof != null)            return instance;        else            return null;    }     public ImmutableDescriptor get(ImmutableDescriptor descriptor) {        WeakReference<ImmutableDescriptor> wr = map.get(descriptor);        ImmutableDescriptor got = (wr == null) ? null : wr.get();        if (got != null)            return got;        map.put(descriptor, new WeakReference<ImmutableDescriptor>(descriptor));        return descriptor;    }     public ImmutableDescriptor union(Descriptor... descriptors) {        return get(ImmutableDescriptor.union(descriptors));    }     private final static DescriptorCache instance = new DescriptorCache();    private final WeakHashMap<ImmutableDescriptor,                              WeakReference<ImmutableDescriptor>>        map = new WeakHashMap<ImmutableDescriptor,                              WeakReference<ImmutableDescriptor>>();}