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Java 1.6+ Library with tons of utility classes required in all projects

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/**
 * Copyright (C) 2014-2016 Philip Helger (www.helger.com)
 * philip[at]helger[dot]com
 *
 * 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.helger.commons.collection.multimap;

import java.util.Map;

import javax.annotation.Nonnull;
import javax.annotation.Nullable;
import javax.annotation.concurrent.NotThreadSafe;

import com.helger.commons.annotation.ReturnsMutableCopy;
import com.helger.commons.annotation.ReturnsMutableObject;
import com.helger.commons.collection.ext.CommonsConcurrentHashMap;
import com.helger.commons.collection.ext.ICommonsCollection;

/**
 * Abstract multi map based on {@link java.util.concurrent.ConcurrentHashMap}.
 * 

 * Important note: null keys are not allowed here!
 *
 * @author Philip Helger
 * @param 
 *        key type
 * @param 
 *        value type
 * @param 
 *        contained collection type
 */
@NotThreadSafe
public abstract class AbstractMultiConcurrentHashMap >
                                                     extends CommonsConcurrentHashMap 
                                                     implements IMultiMap 
{
  public AbstractMultiConcurrentHashMap ()
  {}

  public AbstractMultiConcurrentHashMap (@Nonnull final KEYTYPE aKey, @Nullable final VALUETYPE aValue)
  {
    putSingle (aKey, aValue);
  }

  public AbstractMultiConcurrentHashMap (@Nonnull final KEYTYPE aKey, @Nonnull final COLLTYPE aCollection)
  {
    put (aKey, aCollection);
  }

  public AbstractMultiConcurrentHashMap (@Nullable final Map  aCont)
  {
    if (aCont != null)
      putAll (aCont);
  }

  @Nonnull
  @ReturnsMutableCopy
  protected abstract COLLTYPE createNewCollection ();

  @Nonnull
  @ReturnsMutableObject ("design")
  public COLLTYPE getOrCreate (@Nonnull final KEYTYPE aKey)
  {
    return computeIfAbsent (aKey, k -> createNewCollection ());
  }
}