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package java.util; |
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/** |
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* An unbounded priority {@linkplain Queue queue} based on a priority heap. |
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* This queue orders elements according to an order specified at construction |
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* time, which is specified in the same manner as {@link java.util.TreeSet} |
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* and {@link java.util.TreeMap}: elements are ordered either according to |
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* their <i>natural order</i> (see {@link Comparable}), or according to a |
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* {@link java.util.Comparator}, depending on which constructor is used. |
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* <p>The <em>head</em> of this queue is the <em>least</em> element with |
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* respect to the specified ordering. If multiple elements are tied for least |
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* value, the head is one of those elements. A priority queue does not permit |
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* <tt>null</tt> elements. |
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* An unbounded priority {@linkplain Queue queue} based on a priority |
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* heap. This queue orders elements according to an order specified |
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* at construction time, which is specified either according to their |
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* <i>natural order</i> (see {@link Comparable}), or according to a |
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* {@link java.util.Comparator}, depending on which constructor is |
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* used. A priority queue does not permit <tt>null</tt> elements. |
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* A priority queue relying on natural ordering also does not |
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* permit insertion of non-comparable objects (doing so may result |
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* in <tt>ClassCastException</tt>). |
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* |
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* <p>The {@link #remove()} and {@link #poll()} methods remove and |
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* return the head of the queue. |
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* <p>The <em>head</em> of this queue is the <em>least</em> element |
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* with respect to the specified ordering. If multiple elements are |
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* tied for least value, the head is one of those elements -- ties are |
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* broken arbitrarily. The queue retrieval operations <tt>poll</tt>, |
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* <tt>remove</tt>, <tt>peek</tt>, and <tt>element</tt> access the |
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* element at the head of the queue. |
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* |
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* <p>The {@link #element()} and {@link #peek()} methods return, but do |
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* not delete, the head of the queue. |
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* <p>A priority queue is unbounded, but has an internal |
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* <i>capacity</i> governing the size of an array used to store the |
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* elements on the queue. It is always at least as large as the queue |
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* size. As elements are added to a priority queue, its capacity |
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* grows automatically. The details of the growth policy are not |
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* specified. |
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* |
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* <p>A priority queue has a <i>capacity</i>. The capacity is the |
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* size of the array used internally to store the elements on the |
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* queue. |
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* It is always at least as large as the queue size. As |
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* elements are added to a priority queue, its capacity grows |
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* automatically. The details of the growth policy are not specified. |
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* |
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* <p>The Iterator provided in method {@link #iterator()} is <em>not</em> |
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* <p>This class implements all of the <em>optional</em> methods of |
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* the {@link Collection} and {@link Iterator} interfaces. The |
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* Iterator provided in method {@link #iterator()} is <em>not</em> |
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* guaranteed to traverse the elements of the PriorityQueue in any |
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* particular order. If you need ordered traversal, consider using |
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* <tt>Arrays.sort(pq.toArray())</tt>. |
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} |
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// Queue Methods |
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/** |
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* Add the specified element to this priority queue. |
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* Inserts the specified element into this priority queue. |
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* |
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* @return <tt>true</tt> |
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* @throws ClassCastException if the specified element cannot be compared |
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return true; |
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} |
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public E poll() { |
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public E peek() { |
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if (size == 0) |
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return null; |
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return remove(); |
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} |
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public E peek() { |
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return (E) queue[1]; |
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} |
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* @return <tt>true</tt> (as per the general contract of |
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* <tt>Collection.add</tt>). |
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* |
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* @throws NullPointerException {@inheritDoc} |
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* @throws NullPointerException if the specified element is <tt>null</tt>. |
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* @throws ClassCastException if the specified element cannot be compared |
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* with elements currently in the priority queue according |
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* to the priority queue's ordering. |
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*/ |
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public boolean add(E o) { |
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return super.add(o); |
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return offer(o); |
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} |
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/** |
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* Adds all of the elements in the specified collection to this queue. |
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* The behavior of this operation is undefined if |
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* the specified collection is modified while the operation is in |
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* progress. (This implies that the behavior of this call is undefined if |
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* the specified collection is this queue, and this queue is nonempty.) |
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* <p> |
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* This implementation iterates over the specified collection, and adds |
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* each object returned by the iterator to this collection, in turn. |
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* @throws NullPointerException {@inheritDoc} |
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* @throws ClassCastException if any element cannot be compared |
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* with elements currently in the priority queue according |
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* to the priority queue's ordering. |
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*/ |
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public boolean addAll(Collection<? extends E> c) { |
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return super.addAll(c); |
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} |
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/** |
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* Removes a single instance of the specified element from this |
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* queue, if it is present. More formally, |
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* removes an element <tt>e</tt> such that <tt>(o==null ? e==null : |
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* o.equals(e))</tt>, if the queue contains one or more such |
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* elements. Returns <tt>true</tt> if the queue contained the |
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* specified element (or equivalently, if the queue changed as a |
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* result of the call). |
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* |
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* <p>This implementation iterates over the queue looking for the |
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* specified element. If it finds the element, it removes the element |
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* from the queue using the iterator's remove method.<p> |
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* |
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*/ |
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public boolean remove(Object o) { |
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if (o == null) |
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return false; |
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size = 0; |
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} |
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/** |
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* Removes and returns the first element from queue. |
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*/ |
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public E remove() { |
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> |
public E poll() { |
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if (size == 0) |
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throw new NoSuchElementException(); |
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return null; |
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modCount++; |
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|
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E result = (E) queue[1]; |
