edu.emory.mathcs.backport.java.util
public class PriorityQueue extends AbstractQueue implements Serializable
While this queue is logically unbounded, attempted additions may fail due to resource exhaustion (causing OutOfMemoryError). This class does not permit null elements. A priority queue relying on Comparable natural ordering also does not permit insertion of non-comparable objects (doing so results in ClassCastException).
This class and its iterator implement all of the optional methods of the Collection and Iterator interfaces. The Iterator provided in method iterator is not guaranteed to traverse the elements of the PriorityQueue in any particular order. If you need ordered traversal, consider using Arrays.sort(pq.toArray()).
Operations on this class make no guarantees about the ordering of elements with equal priority. If you need to enforce an ordering, you can define custom classes or comparators that use a secondary key to break ties in primary priority values. See PriorityBlockingQueue for an example.
Implementation note: basic mutative methods (insert, offer, remove, poll etc) have complexity O(log(n)). Parameterless inspection methods (peek, element,isEmpty) have complexity O(1). Methods contains(Object) and remove(Object) have complexity O(n).
Since: 1.5
Constructor Summary | |
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PriorityQueue()
Creates a PriorityQueue with the default
initial capacity (11) that orders its elements according to
their Comparable natural ordering. | |
PriorityQueue(int initialCapacity)
Creates a PriorityQueue with the specified
initial capacity that orders its elements according to their
Comparable natural ordering.
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PriorityQueue(Comparator comparator)
Creates a PriorityQueue with the specified initial
capacity that orders its elements according to the specified
comparator.
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PriorityQueue(int initialCapacity, Comparator comparator) | |
PriorityQueue(PriorityQueue q)
Creates a PriorityQueue containing the elements from
the specified priority queue. | |
PriorityQueue(SortedSet s)
Creates a PriorityQueue containing the elements
from the specified sorted set. | |
PriorityQueue(Collection c)
Creates a PriorityQueue containing the elements
in the specified collection. |
Method Summary | |
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boolean | add(Object o)
Inserts the specified element into this priority queue.
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void | clear()
Removes all of the elements from this queue.
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Comparator | comparator()
Returns the comparator used to order the elements in this queue,
or null if this queue uses the Comparable
natural ordering of its elements.
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boolean | contains(Object o)
Returns true if this queue contains the specified element.
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Object | element()
Retrieves, but does not remove, the head of this queue.
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boolean | isEmpty()
Returns true if this queue contains no elements.
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Iterator | iterator()
Returns an iterator over the elements in this queue. |
boolean | offer(Object o)
Inserts the specified element into this priority queue.
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Object | peek()
Retrieves, but does not remove, the head of this queue, or returns
null if this queue is empty.
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Object | poll()
Retrieves and removes the head of this queue, or returns null
if this queue is empty.
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Object | remove()
Retrieves and removes the head of this queue.
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boolean | remove(Object o)
Removes a single instance of the specified element from this queue,
if it is present.
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int | size()
Returns the number of elements in this priority queue.
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Object[] | toArray()
Returns an array containing all of the elements in this queue.
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Object[] | toArray(Object[] a)
Returns an array containing all of the elements in this queue; the
runtime type of the returned array is that of the specified array.
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Parameters: initialCapacity the initial capacity for this priority queue
Throws: IllegalArgumentException if initialCapacity is less than 1
Parameters: comparator the comparator used to order this priority queue. If null then the order depends on the elements' natural ordering.
Throws: IllegalArgumentException if initialCapacity is less than 1
Parameters: q the queue whose elements are to be placed into this priority queue.
Throws: NullPointerException if the specified queue is null
Parameters: s the set whose elements are to be placed into this priority queue.
Throws: NullPointerException if the specified set or any of its elements are null
Parameters: c the collection whose elements are to be placed into this priority queue.
Throws: ClassCastException if elements of the specified collection cannot be compared to one another according to the priority queue's ordering. NullPointerException if the specified collection or any of its elements are null
Parameters: o the element to add
Returns: true (as per the spec for Collection#add)
Throws: ClassCastException if the specified element cannot be compared with elements currently in the priority queue according to the priority queue's ordering NullPointerException if the specified element is null
Returns: the comparator used to order the elements in this queue, or null if this queue uses the natural ordering of its elements.
Parameters: o object to be checked for containment in this queue
Returns: true if this queue contains the specified element
Returns: the head of this queue
Throws: NoSuchElementException of the queue is empty
Returns: true if this queue contains no elements
Returns: an iterator over the elements in this queue
Parameters: o the element to add
Returns: true (as per the spec for Queue)
Throws: ClassCastException if the specified element cannot be compared with elements currently in the priority queue according to the priority queue's ordering NullPointerException if the specified element is null
Returns: the head of this queue, or null if this queue is empty
Returns: the head of this queue, or null if this queue is empty
Returns: the head of this queue
Parameters: o element to be removed from this queue, if present
Returns: true if this queue changed as a result of the call
Returns: the number of elements in this priority queue
The returned array will be "safe" in that no references to it are maintained by this queue. (In other words, this method must allocate a new array). The caller is thus free to modify the returned array.
This method acts as bridge between array-based and collection-based APIs.
Returns: an array containing all of the elements in this queue
If this queue fits in the specified array with room to spare (i.e., the array has more elements than this queue), the element in the array immediately following the end of the queue is set to null.
Like the toArray method, this method acts as bridge between array-based and collection-based APIs. Further, this method allows precise control over the runtime type of the output array, and may, under certain circumstances, be used to save allocation costs.
Suppose x is a queue known to contain only strings. The following code can be used to dump the queue into a newly allocated array of String:
String[] y = x.toArray(new String[0]);Note that toArray(new Object[0]) is identical in function to toArray().
Parameters: a the array into which the elements of the queue are to be stored, if it is big enough; otherwise, a new array of the same runtime type is allocated for this purpose
Returns: an array containing all of the elements in this queue
Throws: ArrayStoreException if the runtime type of the specified array is not a supertype of the runtime type of every element in this queue NullPointerException if the specified array is null