Class PriorityQueue<E extends java.lang.Comparable<E>>
- java.lang.Object
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- gaia.cu9.ari.gaiaorbit.event.PriorityQueue<E>
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- Type Parameters:
E
- the type of comparable elements held in this queue
public class PriorityQueue<E extends java.lang.Comparable<E>> extends java.lang.Object
An unbounded priority queue based on a priority heap. The elements of the priority queue are ordered according to their natural ordering. A priority queue does not permitnull
elements.The queue can be set to accept or reject the insertion of non unique elements through the method
setUniqueness
. Uniqueness is disabled by default.The head of this queue is the least element with respect to the specified ordering. If multiple elements are tied for least value (provided that uniqueness is set to false), the head is one of those elements -- ties are broken arbitrarily. The queue retrieval operations
poll
,remove
,peek
, andelement
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.
Iterating the queue with the method
get
is not guaranteed to traverse the elements of the priority queue in any particular order.Implementation note: this implementation provides O(log(n)) time for the enqueing and dequeing methods (
add
andpoll
; and constant time for the retrieval methods (peek
andsize
).
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Constructor Summary
Constructors Constructor Description PriorityQueue()
Creates aPriorityQueue
with the default initial capacity (11) that orders its elements according to their natural ordering.PriorityQueue(int initialCapacity)
Creates aPriorityQueue
with the specified initial capacity that orders its elements according to their natural ordering.
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description boolean
add(E e)
Inserts the specified element into this priority queue.void
clear()
Removes all of the elements from this priority queue.E
get(int index)
Retrieves the element at the specified index.boolean
getUniqueness()
Returns a value indicating whether only unique elements are allowed to be inserted.E
peek()
Retrieves, but does not remove, the head of this queue.E
poll()
Retrieves and removes the head of this queue, or returnsnull
if this queue is empty.void
setUniqueness(boolean uniqueness)
Sets a flag indicating whether only unique elements are allowed to be inserted.int
size()
Returns the number of elements in this queue.
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Constructor Detail
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PriorityQueue
public PriorityQueue()
Creates aPriorityQueue
with the default initial capacity (11) that orders its elements according to their natural ordering.
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PriorityQueue
public PriorityQueue(int initialCapacity)
Creates aPriorityQueue
with the specified initial capacity that orders its elements according to their natural ordering.- Parameters:
initialCapacity
- the initial capacity for this priority queue
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Method Detail
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getUniqueness
public boolean getUniqueness()
Returns a value indicating whether only unique elements are allowed to be inserted.
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setUniqueness
public void setUniqueness(boolean uniqueness)
Sets a flag indicating whether only unique elements are allowed to be inserted.
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add
public boolean add(E e)
Inserts the specified element into this priority queue. Ifuniqueness
is enabled and this priority queue already contains the element, the call leaves the queue unchanged and returns false.- Returns:
- true if the element was added to this queue, else false
- Throws:
java.lang.ClassCastException
- if the specified element cannot be compared with elements currently in this priority queue according to the priority queue's orderingjava.lang.NullPointerException
- if the specified element is null
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peek
public E peek()
Retrieves, but does not remove, the head of this queue. If this queue is emptynull
is returned.- Returns:
- the head of this queue
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get
public E get(int index)
Retrieves the element at the specified index. If such an element doesn't existnull
is returned.Iterating the queue by index is not guaranteed to traverse the elements in any particular order.
- Returns:
- the element at the specified index in this queue.
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size
public int size()
Returns the number of elements in this queue.
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clear
public void clear()
Removes all of the elements from this priority queue. The queue will be empty after this call returns.
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poll
public E poll()
Retrieves and removes the head of this queue, or returnsnull
if this queue is empty.- Returns:
- the head of this queue, or
null
if this queue is empty.
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