Added in API level 1

PriorityBlockingQueue

open class PriorityBlockingQueue<E : Any!> : AbstractQueue<E>, BlockingQueue<E>, Serializable

kotlin.Any
↳	java.util.AbstractCollection<E>
	↳	java.util.AbstractQueue<E>
		↳	java.util.concurrent.PriorityBlockingQueue

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&lt;E extends Comparable&lt;? super E&gt;&gt;
      implements Comparable&lt;FIFOEntry&lt;E&gt;&gt; {
    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&lt;E&gt; other) {
      int res = entry.compareTo(other.entry);
      if (res == 0 &amp;&amp; other.entry != this.entry)
        res = (seqNum &lt; other.seqNum ? -1 : 1);
      return res;
    }
  }</code>

This class is a member of the Java Collections Framework.

Summary

Public constructors
`PriorityBlockingQueue()` Creates a `PriorityBlockingQueue` with the default initial capacity (11) that orders its elements according to their natural ordering.
`PriorityBlockingQueue(initialCapacity: Int)` Creates a `PriorityBlockingQueue` with the specified initial capacity that orders its elements according to their natural ordering.
`PriorityBlockingQueue(initialCapacity: Int, comparator: Comparator<in E>!)` Creates a `PriorityBlockingQueue` with the specified initial capacity that orders its elements according to the specified comparator.
`PriorityBlockingQueue(c: MutableCollection<out E>!)` Creates a `PriorityBlockingQueue` containing the elements in the specified collection.

Public methods
open Boolean	`add(element: E)` Inserts the specified element into this priority queue.
open Unit	`clear()` Atomically removes all of the elements from this queue.
open Comparator<in E>!	`comparator()` Returns the comparator used to order the elements in this queue, or `null` if this queue uses the natural ordering of its elements.
open Boolean	`contains(element: E?)` Returns `true` if this queue contains the specified element.
open Int	`drainTo(c: MutableCollection<in E>!)`
open Int	`drainTo(c: MutableCollection<in E>!, maxElements: Int)`
open Unit	`forEach(action: Consumer<in E>)`
open MutableIterator<E>	`iterator()` Returns an iterator over the elements in this queue.
open Boolean	`offer(e: E)` Inserts the specified element into this priority queue.
open Boolean	`offer(e: E, timeout: Long, unit: TimeUnit!)` Inserts the specified element into this priority queue.
open E?	`peek()`
open E?	`poll()`
open E	`poll(timeout: Long, unit: TimeUnit!)`
open Unit	`put(e: E)` Inserts the specified element into this priority queue.
open Int	`remainingCapacity()` Always returns `Integer.MAX_VALUE` because a `PriorityBlockingQueue` is not capacity constrained.
open Boolean	`remove(element: E?)` Removes a single instance of the specified element from this queue, if it is present.
open Boolean	`removeAll(elements: Collection<E>)`
open Boolean	`removeIf(filter: Predicate<in E>)`
open Boolean	`retainAll(elements: Collection<E>)`
open Spliterator<E>	`spliterator()` Returns a `Spliterator` over the elements in this queue.
open E	`take()`
open Array<Any!>	`toArray()` Returns an array containing all of the elements in this queue.
open Array<T>	`toArray(a: 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.
open String	`toString()`

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.

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.

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.

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)`.
`Boolean`	`containsAll(elements: Collection<E>)` Returns `true` if this collection contains all of the elements in the specified collection.
`Boolean`	`isEmpty()` Returns `true` if this collection contains no elements.
`MutableIterator<E>`	`iterator()` Returns an iterator over the elements contained in this collection.
`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).
`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.
`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.
`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.
`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.
`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)`.

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.

E?

peek()

Retrieves, but does not remove, the head of this queue, or returns null if this queue is empty.

E?

poll()

Retrieves and removes the head of this queue, or returns null if this queue is empty.

Properties
open Int	`size`

Inherited properties

From class AbstractCollection

Int

size

Public constructors

PriorityBlockingQueue

Added in API level 1

PriorityBlockingQueue()

Creates a PriorityBlockingQueue with the default initial capacity (11) that orders its elements according to their natural ordering.

PriorityBlockingQueue

Added in API level 1

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

Added in API level 1

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

Added in API level 1

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

Added in API level 1

open fun add(element: E): Boolean

Inserts the specified element into this priority queue.

Parameters
`e`	the element to add

Return
`Boolean`	`true` (as specified by `Collection#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

Added in API level 1

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

Added in API level 1

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

Added in API level 1

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

Added in API level 1

open fun drainTo(c: MutableCollection<in E>!): Int

Parameters
`c`	MutableCollection<in E>!: the collection to transfer elements into

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

Added in API level 1

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

Added in API level 24

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

Added in API level 1

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.

Return
`MutableIterator<E>`	an iterator over the elements in this queue

offer

Added in API level 1

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

Return
`Boolean`	`true` (as specified by `Queue#offer`)

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

Added in API level 1

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

Return
`Boolean`	`true` (as specified by `BlockingQueue.offer`)

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

Added in API level 1

open fun peek(): E?

Return
`E?`	the head of this queue, or `null` if this queue is empty

poll

Added in API level 1

open fun poll(): E?

Return
`E?`	the head of this queue, or `null` if this queue is empty

poll

Added in API level 1

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

Added in API level 1

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

Added in API level 1

open fun remainingCapacity(): Int

Always returns Integer.MAX_VALUE because a PriorityBlockingQueue is not capacity constrained.

Return
`Int`	`Integer.MAX_VALUE` always

remove

Added in API level 1

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

Added in API level 1

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

Added in API level 24

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

Added in API level 1

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

spliterator

Added in API level 24

open fun spliterator(): Spliterator<E>

Returns a Spliterator over the elements in this queue. The spliterator does not traverse elements in any particular order (the ORDERED characteristic is not reported).

The returned spliterator is weakly consistent.

The Spliterator reports Spliterator#SIZED and Spliterator#NONNULL.

Return
`Spliterator<E>`	a `Spliterator` over the elements in this queue

take

Added in API level 1

open fun take(): E

Return
`E`	the head of this queue

Exceptions
`java.lang.InterruptedException`	if interrupted while waiting

toArray

Added in API level 1

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

Added in API level 1

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

Added in API level 1

open fun toString(): String

Return
`String`	a string representation of the object.

Properties

size

Added in API level 1

open val size: Int

Return
`Int`	the number of elements in this collection