MultiMap.java

  1. /*
  2.  * *************************************************************************************************************************************************************
  3.  *
  4.  * TheseFoolishThings: Miscellaneous utilities
  5.  * http://tidalwave.it/projects/thesefoolishthings
  6.  *
  7.  * Copyright (C) 2009 - 2025 by Tidalwave s.a.s. (http://tidalwave.it)
  8.  *
  9.  * *************************************************************************************************************************************************************
  10.  *
  11.  * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License.
  12.  * You may obtain a copy of the License at
  13.  *
  14.  *     http://www.apache.org/licenses/LICENSE-2.0
  15.  *
  16.  * 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
  17.  * CONDITIONS OF ANY KIND, either express or implied.  See the License for the specific language governing permissions and limitations under the License.
  18.  *
  19.  * *************************************************************************************************************************************************************
  20.  *
  21.  * git clone https://bitbucket.org/tidalwave/thesefoolishthings-src
  22.  * git clone https://github.com/tidalwave-it/thesefoolishthings-src
  23.  *
  24.  * *************************************************************************************************************************************************************
  25.  */
  26. package it.tidalwave.util.impl;

  27. import jakarta.annotation.Nonnull;
  28. import java.util.Collection;
  29. import java.util.Collections;
  30. import java.util.HashMap;
  31. import java.util.HashSet;
  32. import java.util.Set;

  33. /***************************************************************************************************************************************************************
  34.  *
  35.  * @author  Fabrizio Giudici
  36.  *
  37.  **************************************************************************************************************************************************************/
  38. public class MultiMap<K, V> extends HashMap<K, Set<V>>
  39.   {
  40.     private static final long serialVersionUID = 8834342771135005212L;

  41.     public synchronized void add (@Nonnull final K key, @Nonnull final V value)
  42.       {
  43.         internalGetValues(key).add(value);
  44.       }

  45.     public synchronized void addAll (@Nonnull final K key, @Nonnull final Collection<? extends V> values)
  46.       {
  47.         if (!values.isEmpty())
  48.           {
  49.             internalGetValues(key).addAll(values);
  50.           }
  51.       }

  52.     @Nonnull
  53.     public synchronized Set<V> getValues (@Nonnull final K key)
  54.       {
  55.         final var values = get(key);
  56.         return (values == null) ? Collections.emptySet() : Collections.unmodifiableSet(values);
  57.       }

  58.     @Nonnull
  59.     private Set<V> internalGetValues (@Nonnull final K key)
  60.       {
  61.         var values = get(key);

  62.         if (values == null)
  63.           {
  64.             values = new HashSet<>();
  65.             put(key, values);
  66.           }

  67.         return values;
  68.       }
  69.   }