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package it.unimi.dsi.fastutil;
/*
* Copyright (C) 2003-2015 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.
*/
import java.util.Comparator;
import java.util.NoSuchElementException;
import it.unimi.dsi.fastutil.PriorityQueue;
/** 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 extends AbstractPriorityQueue {
protected EmptyPriorityQueue() {}
public void enqueue( Object o ) { throw new UnsupportedOperationException(); }
public Object dequeue() { throw new NoSuchElementException(); }
public boolean isEmpty() { return true; }
public int size() { return 0; }
public void clear() {}
public Object first() { throw new NoSuchElementException(); }
public Object last() { throw new NoSuchElementException(); }
public void changed() { throw new NoSuchElementException(); }
public Comparator comparator() { return null; }
}
/** An empty indirect priority queue (immutable).
*/
public final static EmptyPriorityQueue EMPTY_QUEUE = new EmptyPriorityQueue();
/** A synchronized wrapper class for priority queues. */
public static class SynchronizedPriorityQueue implements PriorityQueue {
public static final long serialVersionUID = -7046029254386353129L;
final protected PriorityQueue q;
final protected 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;
}
public void enqueue( K x ) { synchronized( sync ) { q.enqueue( x ); } }
public K dequeue() { synchronized( sync ) { return q.dequeue(); } }
public K first() { synchronized( sync ) { return q.first(); } }
public K last() { synchronized( sync ) { return q.last(); } }
public boolean isEmpty() { synchronized( sync ) { return q.isEmpty(); } }
public int size() { synchronized( sync ) { return q.size(); } }
public void clear() { synchronized( sync ) { q.clear(); } }
public void changed() { synchronized( sync ) { q.changed(); } }
public Comparator comparator() { synchronized( sync ) { return q.comparator(); } }
}
/** Returns a synchronized priority queue backed by the specified priority 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 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 ); }
}