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   /*
    * Copyright 2012 The Netty Project
    *
    * The Netty Project 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:
    *
    *   https://www.apache.org/licenses/LICENSE-2.0
    *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
   * License for the specific language governing permissions and limitations
   * under the License.
   */
  package io.netty.handler.codec.serialization;
  
  import java.lang.ref.Reference;
  import java.util.Collection;
  import java.util.Map;
  import java.util.Set;
  
  abstract class ReferenceMap<K, V> implements Map<K, V> {
  
      private final Map<K, Reference<V>> delegate;
  
      protected ReferenceMap(Map<K, Reference<V>> delegate) {
          this.delegate = delegate;
      }
  
      abstract Reference<V> fold(V value);
  
      private V unfold(Reference<V> ref) {
          if (ref == null) {
              return null;
          }
  
          return ref.get();
      }
  
      @Override
      public int size() {
          return delegate.size();
      }
  
      @Override
      public boolean isEmpty() {
          return delegate.isEmpty();
      }
  
      @Override
      public boolean containsKey(Object key) {
          return delegate.containsKey(key);
      }
  
      @Override
      public boolean containsValue(Object value) {
          throw new UnsupportedOperationException();
      }
  
      @Override
      public V get(Object key) {
          return unfold(delegate.get(key));
      }
  
      @Override
      public V put(K key, V value) {
          return unfold(delegate.put(key, fold(value)));
      }
  
      @Override
      public V remove(Object key) {
          return unfold(delegate.remove(key));
      }
  
      @Override
      public void putAll(Map<? extends K, ? extends V> m) {
          for (Entry<? extends K, ? extends V> entry : m.entrySet()) {
              delegate.put(entry.getKey(), fold(entry.getValue()));
          }
      }
  
      @Override
      public void clear() {
          delegate.clear();
      }
  
      @Override
      public Set<K> keySet() {
          return delegate.keySet();
      }
  
      @Override
      public Collection<V> values() {
          throw new UnsupportedOperationException();
      }
  
      @Override
      public Set<Entry<K, V>> entrySet() {
         throw new UnsupportedOperationException();
     }
 }