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  /*
   * Copyright (C) 2007 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 java.util.Map;
 import java.util.Set;
 
 import  javax.annotation.Nullable;

A map which forwards all its method calls to another map. Subclasses should override one or more methods to modify the behavior of the backing map as desired per the decorator pattern.

Warning: The methods of ForwardingMap forward indiscriminately to the methods of the delegate. For example, overriding put alone will not change the behavior of putAll, which can lead to unexpected behavior. In this case, you should override putAll as well, either providing your own implementation, or delegating to the provided standardPutAll method.

Each of the standard methods, where appropriate, use Objects.equal to test equality for both keys and values. This may not be the desired behavior for map implementations that use non-standard notions of key equality, such as a SortedMap whose comparator is not consistent with equals.

The standard methods and the collection views they return are not guaranteed to be thread-safe, even when all of the methods that they depend on are thread-safe.

Author(s):
Kevin Bourrillion
Jared Levy
Louis Wasserman
Since:
2.0 (imported from Google Collections Library)
 
 public abstract class ForwardingMap<K, V> extends ForwardingObject
     implements Map<K, V> {
   // TODO(user): identify places where thread safety is actually lost
 
  
Constructor for use by subclasses.
 
   protected ForwardingMap() {}
 
   @Override protected abstract Map<K, V> delegate();
 
   @Override
   public int size() {
     return delegate().size();
   }
 
   @Override
   public boolean isEmpty() {
     return delegate().isEmpty();
   }
 
   @Override
   public V remove(Object object) {
     return delegate().remove(object);
   }
 
   @Override
   public void clear() {
     delegate().clear();
   }
 
   @Override
   public boolean containsKey(Object key) {
     return delegate().containsKey(key);
   }
 
   @Override
   public boolean containsValue(Object value) {
     return delegate().containsValue(value);
   }
 
   @Override
   public V get(Object key) {
    return delegate().get(key);
  }
  public V put(K key, V value) {
    return delegate().put(keyvalue);
  }
  public void putAll(Map<? extends K, ? extends V> map) {
    delegate().putAll(map);
  }
  public Set<K> keySet() {
    return delegate().keySet();
  }
  public Collection<V> values() {
    return delegate().values();
  }
  public Set<Entry<K, V>> entrySet() {
    return delegate().entrySet();
  }
  @Override public boolean equals(@Nullable Object object) {
    return object == this || delegate().equals(object);
  }
  @Override public int hashCode() {
    return delegate().hashCode();
  }

  
A sensible definition of putAll(Map) in terms of put(Object, Object). If you override put(Object, Object), you may wish to override putAll(Map) to forward to this implementation.

Since:
7.0
  @Beta protected void standardPutAll(Map<? extends K, ? extends V> map) {
    Maps.putAllImpl(thismap);
  }

  
A sensible, albeit inefficient, definition of remove in terms of the iterator method of entrySet. If you override entrySet, you may wish to override remove to forward to this implementation.

Alternately, you may wish to override remove with keySet().remove, assuming that approach would not lead to an infinite loop.

Since:
7.0
  @Beta protected V standardRemove(@Nullable Object key) {
    Iterator<Entry<K, V>> entryIterator = entrySet().iterator();
    while (entryIterator.hasNext()) {
      Entry<K, V> entry = entryIterator.next();
      if (Objects.equal(entry.getKey(), key)) {
        V value = entry.getValue();
        entryIterator.remove();
        return value;
      }
    }
    return null;
  }

  
A sensible definition of clear in terms of the iterator method of entrySet. In many cases, you may wish to override clear to forward to this implementation.

Since:
7.0
  @Beta protected void standardClear() {
    Iterator<Entry<K, V>> entryIterator = entrySet().iterator();
    while (entryIterator.hasNext()) {
      entryIterator.next();
      entryIterator.remove();
    }
  }

  
A sensible implementation of Map.keySet in terms of the following methods: ForwardingMap.clear, ForwardingMap.containsKey, ForwardingMap.isEmpty, ForwardingMap.remove, ForwardingMap.size, and the Set.iterator method of ForwardingMap.entrySet. In many cases, you may wish to override ForwardingMap.keySet to forward to this implementation or a subclass thereof.

Since:
10.0
  @Beta
  protected class StandardKeySet extends Maps.KeySet<K, V> {
    
Constructor for use by subclasses.
    public StandardKeySet() {}
    @Override
    Map<K, V> map() {
      return ForwardingMap.this;
    }
  }

  
A sensible, albeit inefficient, definition of containsKey in terms of the iterator method of entrySet. If you override entrySet, you may wish to override containsKey to forward to this implementation.

Since:
7.0
  @Beta protected boolean standardContainsKey(@Nullable Object key) {
    return Maps.containsKeyImpl(thiskey);
  }

  
A sensible implementation of Map.values in terms of the following methods: ForwardingMap.clear, ForwardingMap.containsValue, ForwardingMap.isEmpty, ForwardingMap.size, and the Set.iterator method of ForwardingMap.entrySet. In many cases, you may wish to override ForwardingMap.values to forward to this implementation or a subclass thereof.

Since:
10.0
  @Beta
  protected class StandardValues extends Maps.Values<K, V> {
    
Constructor for use by subclasses.
    public StandardValues() {}
    @Override
    Map<K, V> map() {
      return ForwardingMap.this;
    }
  }

  
A sensible definition of containsValue in terms of the iterator method of entrySet. If you override entrySet, you may wish to override containsValue to forward to this implementation.

Since:
7.0
  @Beta protected boolean standardContainsValue(@Nullable Object value) {
    return Maps.containsValueImpl(thisvalue);
  }

  
A sensible implementation of Map.entrySet in terms of the following methods: ForwardingMap.clear, ForwardingMap.containsKey, ForwardingMap.get, ForwardingMap.isEmpty, ForwardingMap.remove, and ForwardingMap.size. In many cases, you may wish to override entrySet to forward to this implementation or a subclass thereof.

Since:
10.0
  @Beta
  protected abstract class StandardEntrySet extends Maps.EntrySet<K, V> {
    
Constructor for use by subclasses.
    public StandardEntrySet() {}
    @Override
    Map<K, V> map() {
      return ForwardingMap.this;
    }
  }

  
A sensible definition of isEmpty in terms of the iterator method of entrySet. If you override entrySet, you may wish to override isEmpty to forward to this implementation.

Since:
7.0
  @Beta protected boolean standardIsEmpty() {
    return !entrySet().iterator().hasNext();
  }

  
A sensible definition of equals in terms of the equals method of entrySet. If you override entrySet, you may wish to override equals to forward to this implementation.

Since:
7.0
  @Beta protected boolean standardEquals(@Nullable Object object) {
    return Maps.equalsImpl(thisobject);
  }

  
A sensible definition of hashCode in terms of the iterator method of entrySet. If you override entrySet, you may wish to override hashCode to forward to this implementation.

Since:
7.0
  @Beta protected int standardHashCode() {
    return Sets.hashCodeImpl(entrySet());
  }

  
A sensible definition of toString in terms of the iterator method of entrySet. If you override entrySet, you may wish to override toString to forward to this implementation.

Since:
7.0
  @Beta protected String standardToString() {
    return Maps.toStringImpl(this);
  }
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