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   /*
    * Copyright 2017 The Netty Project
    *
    * The Netty Project 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:
    *
    *   https://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 io.netty.util.internal;
  
  import java.util.Collection;
  import java.util.Collections;
  import java.util.Iterator;
  import java.util.NoSuchElementException;
  
  public final class EmptyPriorityQueue<T> implements PriorityQueue<T> {
      private static final PriorityQueue<Object> INSTANCE = new EmptyPriorityQueue<Object>();
  
      private EmptyPriorityQueue() {
      }
  
      /**
       * Returns an unmodifiable empty {@link PriorityQueue}.
       */
      @SuppressWarnings("unchecked")
      public static <V> EmptyPriorityQueue<V> instance() {
          return (EmptyPriorityQueue<V>) INSTANCE;
      }
  
      @Override
      public boolean removeTyped(T node) {
          return false;
      }
  
      @Override
      public boolean containsTyped(T node) {
          return false;
      }
  
      @Override
      public void priorityChanged(T node) {
      }
  
      @Override
      public int size() {
          return 0;
      }
  
      @Override
      public boolean isEmpty() {
          return true;
      }
  
      @Override
      public boolean contains(Object o) {
          return false;
      }
  
      @Override
      public Iterator<T> iterator() {
          return Collections.<T>emptyList().iterator();
      }
  
      @Override
      public Object[] toArray() {
          return EmptyArrays.EMPTY_OBJECTS;
      }
  
      @Override
      public <T1> T1[] toArray(T1[] a) {
          if (a.length > 0) {
              a[0] = null;
          }
          return a;
      }
  
      @Override
      public boolean add(T t) {
          return false;
      }
  
      @Override
      public boolean remove(Object o) {
          return false;
      }
  
      @Override
      public boolean containsAll(Collection<?> c) {
          return false;
      }
  
      @Override
     public boolean addAll(Collection<? extends T> c) {
         return false;
     }
 
     @Override
     public boolean removeAll(Collection<?> c) {
         return false;
     }
 
     @Override
     public boolean retainAll(Collection<?> c) {
         return false;
     }
 
     @Override
     public void clear() {
     }
 
     @Override
     public void clearIgnoringIndexes() {
     }
 
     @Override
     public boolean equals(Object o) {
         return o instanceof PriorityQueue && ((PriorityQueue) o).isEmpty();
     }
 
     @Override
     public int hashCode() {
         return 0;
     }
 
     @Override
     public boolean offer(T t) {
         return false;
     }
 
     @Override
     public T remove() {
         throw new NoSuchElementException();
     }
 
     @Override
     public T poll() {
         return null;
     }
 
     @Override
     public T element() {
         throw new NoSuchElementException();
     }
 
     @Override
     public T peek() {
         return null;
     }
 
     @Override
     public String toString() {
         return EmptyPriorityQueue.class.getSimpleName();
     }
 }