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/*
* Copyright (C) 2003-2021 Sebastiano Vigna
*
* 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 it.unimi.dsi.fastutil;
import java.io.Serializable;
import java.util.Comparator;
import java.util.NoSuchElementException;
/** A class providing static methods and objects that do useful things with priority queues.
*
* @see it.unimi.dsi.fastutil.PriorityQueue
*/
public class PriorityQueues {
private PriorityQueues() {}
/** An immutable class representing the empty priority queue.
*
* This class may be useful to implement your own in case you subclass
* {@link PriorityQueue}.
*/
@SuppressWarnings("rawtypes")
public static class EmptyPriorityQueue implements PriorityQueue, Serializable {
private static final long serialVersionUID = 0L;
protected EmptyPriorityQueue() {}
@Override
public void enqueue(final Object o) { throw new UnsupportedOperationException(); }
@Override
public Object dequeue() { throw new NoSuchElementException(); }
@Override
public boolean isEmpty() { return true; }
@Override
public int size() { return 0; }
@Override
public void clear() {}
@Override
public Object first() { throw new NoSuchElementException(); }
@Override
public Object last() { throw new NoSuchElementException(); }
@Override
public void changed() { throw new NoSuchElementException(); }
@Override
public Comparator comparator() { return null; }
@Override
public Object clone() { return EMPTY_QUEUE; }
@Override
public int hashCode() { return 0; }
@Override
public boolean equals(final Object o) { return o instanceof PriorityQueue && ((PriorityQueue)o).isEmpty(); }
private Object readResolve() { return EMPTY_QUEUE; }
}
/** An empty indirect priority queue (immutable). */
public static final EmptyPriorityQueue EMPTY_QUEUE = new EmptyPriorityQueue();
/** Returns an empty queue (immutable). It is serializable and cloneable.
*
*
This method provides a typesafe access to {@link #EMPTY_QUEUE}.
* @param the class of the objects in the queue.
* @return an empty queue (immutable).
*/
@SuppressWarnings("unchecked")
public static PriorityQueue emptyQueue() {
return EMPTY_QUEUE;
}
/** A synchronized wrapper class for priority queues. */
public static class SynchronizedPriorityQueue implements PriorityQueue, Serializable {
public static final long serialVersionUID = -7046029254386353129L;
protected final PriorityQueue q;
protected final Object sync;
protected SynchronizedPriorityQueue(final PriorityQueue q, final Object sync) {
this.q = q;
this.sync = sync;
}
protected SynchronizedPriorityQueue(final PriorityQueue q) {
this.q = q;
this.sync = this;
}
@Override
public void enqueue(final K x) { synchronized(sync) { q.enqueue(x); } }
@Override
public K dequeue() { synchronized(sync) { return q.dequeue(); } }
@Override
public K first() { synchronized(sync) { return q.first(); } }
@Override
public K last() { synchronized(sync) { return q.last(); } }
@Override
public boolean isEmpty() { synchronized(sync) { return q.isEmpty(); } }
@Override
public int size() { synchronized(sync) { return q.size(); } }
@Override
public void clear() { synchronized(sync) { q.clear(); } }
@Override
public void changed() { synchronized(sync) { q.changed(); } }
@Override
public Comparator comparator() { synchronized(sync) { return q.comparator(); } }
@Override
public String toString() { synchronized(sync) { return q.toString(); } }
@Override
public int hashCode() { synchronized(sync) { return q.hashCode(); } }
@Override
public boolean equals(final Object o) { if (o == this) return true; synchronized(sync) { return q.equals(o); } }
private void writeObject(final java.io.ObjectOutputStream s) throws java.io.IOException {
synchronized(sync) { s.defaultWriteObject(); }
}
}
/** Returns a synchronized priority queue backed by the specified priority queue.
*
* @param the class of the objects in the queue.
* @param q the priority queue to be wrapped in a synchronized priority queue.
* @return a synchronized view of the specified priority queue.
*/
public static PriorityQueue synchronize(final PriorityQueue q) { return new SynchronizedPriorityQueue<>(q); }
/** Returns a synchronized priority queue backed by the specified priority queue, using an assigned object to synchronize.
*
* @param the class of the objects in the queue.
* @param q the priority queue to be wrapped in a synchronized priority queue.
* @param sync an object that will be used to synchronize the access to the priority queue.
* @return a synchronized view of the specified priority queue.
*/
public static PriorityQueue synchronize(final PriorityQueue q, final Object sync) { return new SynchronizedPriorityQueue<>(q, sync); }
}