java.lang.Object
java.util.AbstractCollection<E>
java.util.AbstractQueue<E>
java.util.PriorityQueue<E>
E - the type of elements held in this collection
public class PriorityQueue<E>
An unbounded priority queue based on a priority heap. This queue orders elements according to an order specified at construction time, which is specified either according to their natural order (see Comparable), or according to a Comparator, depending on which constructor is used. A priority queue does not permit null elements. A priority queue relying on natural ordering also does not permit insertion of non-comparable objects (doing so may result in ClassCastException).
The head of this queue is the least element with respect to the specified ordering. If multiple elements are tied for least value, the head is one of those elements -- ties are broken arbitrarily. The queue retrieval operations poll, remove, peek, and element access the element at the head of the queue.
A priority queue is unbounded, but has an internal capacity governing the size of an array used to store the elements on the queue. It is always at least as large as the queue size. As elements are added to a priority queue, its capacity grows automatically. The details of the growth policy are not specified.
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()).
Note that this implementation is not synchronized. Multiple threads should not access a PriorityQueue instance concurrently if any of the threads modifies the list structurally. Instead, use the thread-safe PriorityBlockingQueue class.
Implementation note: this implementation provides O(log(n)) time for the insertion methods (offer, poll, remove() and add) methods; linear time for the remove(Object) and contains(Object) methods; and constant time for the retrieval methods (peek, element, and size).
This class is a member of the Java Collections Framework.
PriorityQueue()
PriorityQueue(Collection<? extends E> c)
PriorityQueue(int initialCapacity)
PriorityQueue(int initialCapacity, Comparator<? super E> comparator)
PriorityQueue(PriorityQueue<? extends E> c)
PriorityQueue(SortedSet<? extends E> c)
boolean add(E o)
void clear()
Comparator<? super E> comparator()
Iterator<E> iterator()
boolean offer(E o)
E peek()
E poll()
boolean remove(Object o)
int size()
public PriorityQueue()
public PriorityQueue(int initialCapacity)
initialCapacity - the initial capacity for this priority queue.
IllegalArgumentException - if initialCapacity is less than 1
public PriorityQueue(int initialCapacity,
Comparator<? super E> comparator)
initialCapacity - the initial capacity for this priority queue.
comparator - the comparator used to order this priority queue. If null then the order depends on the elements' natural ordering.
IllegalArgumentException - if initialCapacity is less than 1
public PriorityQueue(Collection<? extends E> c)
SortedSet or is another PriorityQueue, the priority queue will be sorted according to the same comparator, or according to its elements' natural order if the collection is sorted according to its elements' natural order. Otherwise, the priority queue is ordered according to its elements' natural order.
c - the collection whose elements are to be placed into this priority queue.
ClassCastException - if elements of the specified collection cannot be compared to one another according to the priority queue's ordering.
NullPointerException - if c or any element within it is null
public PriorityQueue(PriorityQueue<? extends E> c)
c - the collection whose elements are to be placed into this priority queue.
ClassCastException - if elements of the specified collection cannot be compared to one another according to the priority queue's ordering.
NullPointerException - if c or any element within it is null
public PriorityQueue(SortedSet<? extends E> c)
c - the collection whose elements are to be placed into this priority queue.
ClassCastException - if elements of the specified collection cannot be compared to one another according to the priority queue's ordering.
NullPointerException - if c or any element within it is null
public boolean offer(E o)
offer in interface Queue<E>
o - the element to insert.
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.
public E peek()
Queue
peek in interface Queue<E>
public boolean add(E o)
add in interface Collection<E>
add in class AbstractQueue<E>
o - the element
NullPointerException - if the specified element is null.
ClassCastException - if the specified element cannot be compared with elements currently in the priority queue according to the priority queue's ordering.
public boolean remove(Object o)
remove in interface Collection<E>
remove in class AbstractCollection<E>
o - element to be removed from this collection, if present.
public Iterator<E> iterator()
iterator in interface Iterable<E>
iterator in interface Collection<E>
iterator in class AbstractCollection<E>
public int size()
AbstractCollection
size in interface Collection<E>
size in class AbstractCollection<E>
public void clear()
clear in interface Collection<E>
clear in class AbstractQueue<E>
public E poll()
Queue
poll in interface Queue<E>
public Comparator<? super E> comparator()
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