content: /*
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements. See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF 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
   *
   *     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 org.apache.activemq.artemis.utils.collections;
  
  import java.util.AbstractMap;
  import java.util.Collection;
  import java.util.Collections;
  import java.util.Map;
  import java.util.Set;
  
  /**
   * This class implements a Map, but actually doesnt store anything, it is similar in idea to an EmptyMap, but where
   * mutation methods simply do a no op rather than UnsupportedOperationException as with EmptyMap.
   * <p>
   * This is used in QueueImpl when message groups is disabled.
   *
   * @param <K> the key type.
   * @param <V> the value type.
   */
  public class NoOpMap<K, V> extends AbstractMap<K, V> {
  
     private static final Map NO_OP_MAP = new NoOpMap<>();
  
     @SuppressWarnings("unchecked")
     public static <K, V> Map<K, V> instance() {
        return (Map<K, V>) NO_OP_MAP;
     }
  
     private NoOpMap() {
     }
  
     @Override
     public V put(K key, V value) {
        return null;
     }
  
     @Override
     public int size() {
        return 0;
     }
  
     @Override
     public boolean isEmpty() {
        return true;
     }
  
     @Override
     public boolean containsKey(Object key) {
        return false;
     }
  
     @Override
     public boolean containsValue(Object value) {
        return false;
     }
  
     @Override
     public V get(Object key) {
        return null;
     }
  
     @Override
     public Set<K> keySet() {
        return Collections.emptySet();
     }
  
     @Override
     public Collection<V> values() {
        return Collections.emptySet();
     }
  
     @Override
     public Set<Entry<K, V>> entrySet() {
        return Collections.emptySet();
     }
  
     @Override
     public boolean equals(Object obj) {
        return (obj instanceof Map other) && other.isEmpty();
     }
  
     @Override
     public int hashCode() {
        return 0;
     }
  }