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Guava is a suite of core and expanded libraries that include utility classes, google's collections, io classes, and much much more. This project includes GWT-friendly sources.

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/*
 * Copyright (C) 2011 The Guava Authors
 *
 * Licensed 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
 *
 * 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 com.google.common.collect;

import com.google.common.annotations.GwtCompatible;

import java.util.Map;
import java.util.Set;

/**
 * Workaround for 
 * 
 * EnumMap bug. If you want to pass an {@code EnumMap}, with the
 * intention of using its {@code entrySet()} method, you should
 * wrap the {@code EnumMap} in this class instead. 
 * 
 * @author Dimitris Andreou
 */
@GwtCompatible
final class WellBehavedMap extends ForwardingMap {
  private final Map delegate;
  private Set> entrySet;
  
  private WellBehavedMap(Map delegate) {
    this.delegate = delegate;
  }
  
  /**
   * Wraps the given map into a {@code WellBehavedEntriesMap}, which
   * intercepts its {@code entrySet()} method by taking the 
   * {@code Set keySet()} and transforming it to
   * {@code Set>}. All other invocations are delegated as-is.  
   */
  static  WellBehavedMap wrap(Map delegate) {
    return new WellBehavedMap(delegate);
  }

  @Override protected Map delegate() {
    return delegate;
  }

  @Override public Set> entrySet() {
    Set> es = entrySet;
    if (es != null) {
      return es;
    }
    return entrySet = Sets.transform(
        delegate.keySet(), new KeyToEntryConverter(this));
  }
  
  private static class KeyToEntryConverter 
      extends Sets.InvertibleFunction> {
    final Map map;
    
    KeyToEntryConverter(Map map) {
      this.map = map;
    }

    @Override public Map.Entry apply(final K key) {
      return new AbstractMapEntry() {
        @Override public K getKey() {
          return key;
        }
        @Override public V getValue() {
          return map.get(key);
        }
        @Override public V setValue(V value) {
          return map.put(key, value);
        }
      };
    }

    @Override public K invert(Map.Entry entry) {
      return entry.getKey();
    }
  }
}