PriorityBlockingQueue
open class PriorityBlockingQueue<E : Any!> : AbstractQueue<E>, BlockingQueue<E>, Serializable
An unbounded blocking queue that uses the same ordering rules as class PriorityQueue and supplies blocking retrieval operations. 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 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() and the Spliterator provided in method #spliterator() are not guaranteed to traverse the elements of the PriorityBlockingQueue in any particular order. If you need ordered traversal, consider using Arrays.sort(pq.toArray()). Also, method drainTo can be used to remove some or all elements in priority order and place them in another collection.
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. For example, here is a class that applies first-in-first-out tie-breaking to comparable elements. To use it, you would insert a new FIFOEntry(anEntry) instead of a plain entry object.
<code>class FIFOEntry<E extends Comparable<? super E>>
implements Comparable<FIFOEntry<E>> {
static final AtomicLong seq = new AtomicLong();
final long seqNum;
final E entry;
public FIFOEntry(E entry) {
seqNum = seq.getAndIncrement();
this.entry = entry;
}
public E getEntry() { return entry; }
public int compareTo(FIFOEntry<E> other) {
int res = entry.compareTo(other.entry);
if (res == 0 && other.entry != this.entry)
res = (seqNum < other.seqNum ? -1 : 1);
return res;
}
}</code>
This class is a member of the Java Collections Framework.
Summary
| Public constructors |
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Creates a PriorityBlockingQueue with the default initial capacity (11) that orders its elements according to their natural ordering.
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Creates a PriorityBlockingQueue with the specified initial capacity that orders its elements according to their natural ordering.
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Creates a PriorityBlockingQueue with the specified initial capacity that orders its elements according to the specified comparator.
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Creates a PriorityBlockingQueue containing the elements in the specified collection.
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| Public methods |
| open Boolean |
Inserts the specified element into this priority queue.
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| open Unit |
Atomically removes all of the elements from this queue.
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| open Comparator<in E>! |
Returns the comparator used to order the elements in this queue, or null if this queue uses the natural ordering of its elements.
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| open Boolean |
Returns true if this queue contains the specified element.
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| open Int |
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| open Int |
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| open Unit |
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| open MutableIterator<E> |
Returns an iterator over the elements in this queue.
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| open Boolean |
Inserts the specified element into this priority queue.
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| open Boolean |
Inserts the specified element into this priority queue.
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| open E? |
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| open E? |
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| open E |
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| open Unit |
Inserts the specified element into this priority queue.
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| open Int |
Always returns Integer.MAX_VALUE because a PriorityBlockingQueue is not capacity constrained.
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| open Boolean |
Removes a single instance of the specified element from this queue, if it is present.
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| open Boolean |
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| open Boolean |
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| open Boolean |
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| open Spliterator<E> |
Returns a Spliterator over the elements in this queue.
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| open E |
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| open Array<Any!> |
Returns an array containing all of the elements in this queue.
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| open Array<T> |
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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| open String |
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| Inherited functions |
From class AbstractQueue
Boolean |
addAll(elements: Collection<E>)
Adds all of the elements in the specified collection to this queue. Attempts to addAll of a queue to itself result in IllegalArgumentException. Further, the behavior of this operation is undefined if the specified collection is modified while the operation is in progress.
This implementation iterates over the specified collection, and adds each element returned by the iterator to this queue, in turn. A runtime exception encountered while trying to add an element (including, in particular, a null element) may result in only some of the elements having been successfully added when the associated exception is thrown.
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E |
element()
Retrieves, but does not remove, the head of this queue. This method differs from peek only in that it throws an exception if this queue is empty.
This implementation returns the result of peek unless the queue is empty.
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E |
remove()
Retrieves and removes the head of this queue. This method differs from poll only in that it throws an exception if this queue is empty.
This implementation returns the result of poll unless the queue is empty.
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From class AbstractCollection
Boolean |
contains(element: E?)
Returns true if this collection contains the specified element. More formally, returns true if and only if this collection contains at least one element e such that Objects.equals(o, e).
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Boolean |
containsAll(elements: Collection<E>)
Returns true if this collection contains all of the elements in the specified collection.
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Boolean |
isEmpty()
Returns true if this collection contains no elements.
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MutableIterator<E> |
iterator()
Returns an iterator over the elements contained in this collection.
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Boolean |
remove(element: E?)
Removes a single instance of the specified element from this collection, if it is present (optional operation). More formally, removes an element e such that Objects.equals(o, e), if this collection contains one or more such elements. Returns true if this collection contained the specified element (or equivalently, if this collection changed as a result of the call).
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Boolean |
removeAll(elements: Collection<E>)
Removes all of this collection's elements that are also contained in the specified collection (optional operation). After this call returns, this collection will contain no elements in common with the specified collection.
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Boolean |
retainAll(elements: Collection<E>)
Retains only the elements in this collection that are contained in the specified collection (optional operation). In other words, removes from this collection all of its elements that are not contained in the specified collection.
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Array<Any!> |
toArray()
Returns an array containing all of the elements in this collection. If this collection makes any guarantees as to what order its elements are returned by its iterator, this method must return the elements in the same order. The returned array's runtime component type is Object.
The returned array will be "safe" in that no references to it are maintained by this collection. (In other words, this method must allocate a new array even if this collection is backed by an array). The caller is thus free to modify the returned array.
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Array<T> |
toArray(a: Array<T>)
Returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array. If the collection fits in the specified array, it is returned therein. Otherwise, a new array is allocated with the runtime type of the specified array and the size of this collection.
If this collection fits in the specified array with room to spare (i.e., the array has more elements than this collection), the element in the array immediately following the end of the collection is set to null. (This is useful in determining the length of this collection only if the caller knows that this collection does not contain any null elements.)
If this collection makes any guarantees as to what order its elements are returned by its iterator, this method must return the elements in the same order.
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String |
toString()
Returns a string representation of this collection. The string representation consists of a list of the collection's elements in the order they are returned by its iterator, enclosed in square brackets ("[]"). Adjacent elements are separated by the characters ", " (comma and space). Elements are converted to strings as by String#valueOf(Object).
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From class Queue
Boolean |
offer(e: E)
Inserts the specified element into this queue if it is possible to do so immediately without violating capacity restrictions. When using a capacity-restricted queue, this method is generally preferable to add, which can fail to insert an element only by throwing an exception.
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E? |
peek()
Retrieves, but does not remove, the head of this queue, or returns null if this queue is empty.
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E? |
poll()
Retrieves and removes the head of this queue, or returns null if this queue is empty.
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Public constructors
PriorityBlockingQueue
PriorityBlockingQueue()
Creates a PriorityBlockingQueue with the default initial capacity (11) that orders its elements according to their natural ordering.
PriorityBlockingQueue
PriorityBlockingQueue(initialCapacity: Int)
Creates a PriorityBlockingQueue with the specified initial capacity that orders its elements according to their natural ordering.
| Parameters |
initialCapacity |
Int: the initial capacity for this priority queue |
| Exceptions |
java.lang.IllegalArgumentException |
if initialCapacity is less than 1 |
PriorityBlockingQueue
PriorityBlockingQueue(
initialCapacity: Int,
comparator: Comparator<in E>!)
Creates a PriorityBlockingQueue with the specified initial capacity that orders its elements according to the specified comparator.
| Parameters |
initialCapacity |
Int: the initial capacity for this priority queue |
comparator |
Comparator<in E>!: the comparator that will be used to order this priority queue. If null, the natural ordering of the elements will be used. |
| Exceptions |
java.lang.IllegalArgumentException |
if initialCapacity is less than 1 |
PriorityBlockingQueue
PriorityBlockingQueue(c: MutableCollection<out E>!)
Creates a PriorityBlockingQueue containing the elements in the specified collection. If the specified collection is a SortedSet or a PriorityBlockingQueue, this priority queue will be ordered according to the same ordering. Otherwise, this priority queue will be ordered according to the natural ordering of its elements.
| Parameters |
c |
MutableCollection<out E>!: the collection whose elements are to be placed into this priority queue |
| Exceptions |
java.lang.ClassCastException |
if elements of the specified collection cannot be compared to one another according to the priority queue's ordering |
java.lang.NullPointerException |
if the specified collection or any of its elements are null |
Public methods
add
open fun add(element: E): Boolean
Inserts the specified element into this priority queue.
| Parameters |
e |
the element to add |
| Exceptions |
java.lang.UnsupportedOperationException |
if the add operation is not supported by this collection |
java.lang.ClassCastException |
if the specified element cannot be compared with elements currently in the priority queue according to the priority queue's ordering |
java.lang.NullPointerException |
if the specified element is null |
java.lang.IllegalArgumentException |
if some property of the specified element prevents it from being added to this queue |
java.lang.IllegalStateException |
if the element cannot be added at this time due to capacity restrictions |
clear
open fun clear(): Unit
Atomically removes all of the elements from this queue. The queue will be empty after this call returns.
| Exceptions |
java.lang.UnsupportedOperationException |
if the clear operation is not supported by this collection |
comparator
open fun comparator(): Comparator<in E>!
Returns the comparator used to order the elements in this queue, or null if this queue uses the natural ordering of its elements.
| Return |
Comparator<in E>! |
the comparator used to order the elements in this queue, or null if this queue uses the natural ordering of its elements |
contains
open fun contains(element: E?): Boolean
Returns true if this queue contains the specified element. More formally, returns true if and only if this queue contains at least one element e such that o.equals(e).
| Parameters |
o |
object to be checked for containment in this queue |
| Return |
Boolean |
true if this queue contains the specified element |
| Exceptions |
java.lang.ClassCastException |
if the class of the specified element is incompatible with this queue (optional) |
java.lang.NullPointerException |
if the specified element is null (optional) |
drainTo
open fun drainTo(c: MutableCollection<in E>!): Int
| Return |
Int |
the number of elements transferred |
| Exceptions |
java.lang.UnsupportedOperationException |
if addition of elements is not supported by the specified collection |
java.lang.ClassCastException |
if the class of an element of this queue prevents it from being added to the specified collection |
java.lang.NullPointerException |
if the specified collection is null |
java.lang.IllegalArgumentException |
if the specified collection is this queue, or some property of an element of this queue prevents it from being added to the specified collection |
drainTo
open fun drainTo(
c: MutableCollection<in E>!,
maxElements: Int
): Int
| Parameters |
c |
MutableCollection<in E>!: the collection to transfer elements into |
maxElements |
Int: the maximum number of elements to transfer |
| Return |
Int |
the number of elements transferred |
| Exceptions |
java.lang.UnsupportedOperationException |
if addition of elements is not supported by the specified collection |
java.lang.ClassCastException |
if the class of an element of this queue prevents it from being added to the specified collection |
java.lang.NullPointerException |
if the specified collection is null |
java.lang.IllegalArgumentException |
if the specified collection is this queue, or some property of an element of this queue prevents it from being added to the specified collection |
forEach
open fun forEach(action: Consumer<in E>): Unit
| Parameters |
action |
Consumer<in E>: The action to be performed for each element |
| Exceptions |
java.lang.NullPointerException |
if the specified action is null |
iterator
open fun iterator(): MutableIterator<E>
Returns an iterator over the elements in this queue. The iterator does not return the elements in any particular order.
The returned iterator is weakly consistent.
offer
open fun offer(e: E): Boolean
Inserts the specified element into this priority queue. As the queue is unbounded, this method will never return false.
| Parameters |
e |
E: the element to add |
| Exceptions |
java.lang.ClassCastException |
if the specified element cannot be compared with elements currently in the priority queue according to the priority queue's ordering |
java.lang.NullPointerException |
if the specified element is null |
java.lang.IllegalArgumentException |
if some property of the specified element prevents it from being added to this queue |
offer
open fun offer(
e: E,
timeout: Long,
unit: TimeUnit!
): Boolean
Inserts the specified element into this priority queue. As the queue is unbounded, this method will never block or return false.
| Parameters |
e |
E: the element to add |
timeout |
Long: This parameter is ignored as the method never blocks |
unit |
TimeUnit!: This parameter is ignored as the method never blocks |
| Exceptions |
java.lang.InterruptedException |
if interrupted while waiting |
java.lang.ClassCastException |
if the specified element cannot be compared with elements currently in the priority queue according to the priority queue's ordering |
java.lang.NullPointerException |
if the specified element is null |
java.lang.IllegalArgumentException |
if some property of the specified element prevents it from being added to this queue |
peek
open fun peek(): E?
| Return |
E? |
the head of this queue, or null if this queue is empty |
poll
open fun poll(): E?
| Return |
E? |
the head of this queue, or null if this queue is empty |
poll
open fun poll(
timeout: Long,
unit: TimeUnit!
): E
| Parameters |
timeout |
Long: how long to wait before giving up, in units of unit |
unit |
TimeUnit!: a TimeUnit determining how to interpret the timeout parameter |
| Return |
E |
the head of this queue, or null if the specified waiting time elapses before an element is available |
| Exceptions |
java.lang.InterruptedException |
if interrupted while waiting |
put
open fun put(e: E): Unit
Inserts the specified element into this priority queue. As the queue is unbounded, this method will never block.
| Parameters |
e |
E: the element to add |
| Exceptions |
java.lang.InterruptedException |
if interrupted while waiting |
java.lang.ClassCastException |
if the specified element cannot be compared with elements currently in the priority queue according to the priority queue's ordering |
java.lang.NullPointerException |
if the specified element is null |
java.lang.IllegalArgumentException |
if some property of the specified element prevents it from being added to this queue |
remainingCapacity
open fun remainingCapacity(): Int
Always returns Integer.MAX_VALUE because a PriorityBlockingQueue is not capacity constrained.
| Return |
Int |
Integer.MAX_VALUE always |
remove
open fun remove(element: E?): Boolean
Removes a single instance of the specified element from this queue, if it is present. More formally, removes an element e such that o.equals(e), if this queue contains one or more such elements. Returns true if and only if this queue contained the specified element (or equivalently, if this queue changed as a result of the call).
| Parameters |
o |
element to be removed from this queue, if present |
| Return |
Boolean |
true if this queue changed as a result of the call |
| Exceptions |
java.lang.ClassCastException |
if the class of the specified element is incompatible with this queue (optional) |
java.lang.NullPointerException |
if the specified element is null (optional) |
java.lang.UnsupportedOperationException |
if the remove operation is not supported by this collection |
removeAll
open fun removeAll(elements: Collection<E>): Boolean
| Parameters |
c |
collection containing elements to be removed from this collection |
| Return |
Boolean |
true if this collection changed as a result of the call |
| Exceptions |
java.lang.UnsupportedOperationException |
if the removeAll method is not supported by this collection |
java.lang.ClassCastException |
if the types of one or more elements in this collection are incompatible with the specified collection (optional) |
java.lang.NullPointerException |
if this collection contains one or more null elements and the specified collection does not support null elements (optional), or if the specified collection is null |
removeIf
open fun removeIf(filter: Predicate<in E>): Boolean
| Parameters |
filter |
Predicate<in E>: a predicate which returns true for elements to be removed |
| Return |
Boolean |
true if any elements were removed |
| Exceptions |
java.lang.NullPointerException |
if the specified filter is null |
java.lang.UnsupportedOperationException |
if elements cannot be removed from this collection. Implementations may throw this exception if a matching element cannot be removed or if, in general, removal is not supported. |
retainAll
open fun retainAll(elements: Collection<E>): Boolean
| Parameters |
c |
collection containing elements to be retained in this collection |
| Return |
Boolean |
true if this collection changed as a result of the call |
| Exceptions |
java.lang.UnsupportedOperationException |
if the retainAll operation is not supported by this collection |
java.lang.ClassCastException |
if the types of one or more elements in this collection are incompatible with the specified collection (optional) |
java.lang.NullPointerException |
if this collection contains one or more null elements and the specified collection does not permit null elements (optional), or if the specified collection is null |
take
open fun take(): E
| Return |
E |
the head of this queue |
| Exceptions |
java.lang.InterruptedException |
if interrupted while waiting |
toArray
open fun toArray(): Array<Any!>
Returns an array containing all of the elements in this queue. The returned array elements are in no particular order.
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.
| Return |
Array<Any!> |
an array containing all of the elements in this queue |
toArray
open fun <T : Any!> toArray(a: Array<T>): Array<T>
Returns an array containing all of the elements in this queue; the runtime type of the returned array is that of the specified array. The returned array elements are in no particular order. If the queue fits in the specified array, it is returned therein. Otherwise, a new array is allocated with the runtime type of the specified array and the size of 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:
<code>String[] y = x.toArray(new String[0]);</code>
Note that
toArray(new Object[0]) is identical in function to
toArray().
| Parameters |
<T> |
the component type of the array to contain the collection |
a |
Array<T>: 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 |
| Return |
Array<T> |
an array containing all of the elements in this queue |
| Exceptions |
java.lang.ArrayStoreException |
if the runtime type of the specified array is not a supertype of the runtime type of every element in this queue |
java.lang.NullPointerException |
if the specified array is null |
toString
open fun toString(): String
| Return |
String |
a string representation of the object. |
Properties
size
open val size: Int
| Return |
Int |
the number of elements in this collection |
