Added in API level 1

PriorityQueue

open class PriorityQueue<E : Any!> : AbstractQueue<E>, Serializable

kotlin.Any
↳	java.util.AbstractCollection<E>
	↳	java.util.AbstractQueue<E>
		↳	java.util.PriorityQueue

An unbounded priority queue based on a priority heap. The elements of the priority queue are ordered according to their natural ordering, or by a Comparator provided at queue construction time, 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() and the Spliterator provided in method #spliterator() are not guaranteed to traverse the elements of the priority queue 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 queue. Instead, use the thread-safe class.

Implementation note: this implementation provides O(log(n)) time for the enqueuing and dequeuing methods (offer, poll, remove() and add); 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.

Summary

Public constructors
`PriorityQueue()` Creates a `PriorityQueue` with the default initial capacity (11) that orders its elements according to their natural ordering.
`PriorityQueue(initialCapacity: Int)` Creates a `PriorityQueue` with the specified initial capacity that orders its elements according to their natural ordering.
`PriorityQueue(comparator: Comparator<in E>!)` Creates a `PriorityQueue` with the default initial capacity and whose elements are ordered according to the specified comparator.
`PriorityQueue(initialCapacity: Int, comparator: Comparator<in E>!)` Creates a `PriorityQueue` with the specified initial capacity that orders its elements according to the specified comparator.
`PriorityQueue(c: MutableCollection<out E>!)` Creates a `PriorityQueue` containing the elements in the specified collection.
`PriorityQueue(c: PriorityQueue<out E>!)` Creates a `PriorityQueue` containing the elements in the specified priority queue.
`PriorityQueue(c: SortedSet<out E>!)` Creates a `PriorityQueue` containing the elements in the specified sorted set.

Public methods
open Boolean	`add(element: E)` Inserts the specified element into this priority queue.
open Unit	`clear()` Removes all of the elements from this priority queue.
open Comparator<in E>!	`comparator()` Returns the comparator used to order the elements in this queue, or `null` if this queue is sorted according to the natural ordering of its elements.
open Boolean	`contains(element: E?)` Returns `true` if this queue contains the specified element.
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 E?	`peek()`
open E?	`poll()`
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>)`
Spliterator<E>	`spliterator()` Creates a late-binding and fail-fast `Spliterator` over the elements in this queue.
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.

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

PriorityQueue

Added in API level 1

PriorityQueue()

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

PriorityQueue

Added in API level 1

PriorityQueue(initialCapacity: Int)

Creates a PriorityQueue 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

PriorityQueue

Added in API level 24

PriorityQueue(comparator: Comparator<in E>!)

Creates a PriorityQueue with the default initial capacity and whose elements are ordered according to the specified comparator.

Parameters
`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.

PriorityQueue

Added in API level 1

PriorityQueue(
    initialCapacity: Int, 
    comparator: Comparator<in E>!)

Creates a PriorityQueue 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

PriorityQueue

Added in API level 1

PriorityQueue(c: MutableCollection<out E>!)

Creates a PriorityQueue containing the elements in the specified collection. If the specified collection is an instance of a SortedSet or is another PriorityQueue, 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

PriorityQueue

Added in API level 1

PriorityQueue(c: PriorityQueue<out E>!)

Creates a PriorityQueue containing the elements in the specified priority queue. This priority queue will be ordered according to the same ordering as the given priority queue.

Parameters
`c`	PriorityQueue<out E>!: the priority queue whose elements are to be placed into this priority queue

Exceptions
`java.lang.ClassCastException`	if elements of `c` cannot be compared to one another according to `c`'s ordering
`java.lang.NullPointerException`	if the specified priority queue or any of its elements are null

PriorityQueue

Added in API level 1

PriorityQueue(c: SortedSet<out E>!)

Creates a PriorityQueue containing the elements in the specified sorted set. This priority queue will be ordered according to the same ordering as the given sorted set.

Parameters
`c`	SortedSet<out E>!: the sorted set whose elements are to be placed into this priority queue

Exceptions
`java.lang.ClassCastException`	if elements of the specified sorted set cannot be compared to one another according to the sorted set's ordering
`java.lang.NullPointerException`	if the specified sorted set 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 this 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 this 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

Removes all of the elements from this priority 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 is sorted according to the natural ordering of its elements.

Return
`Comparator<in E>!`	the comparator used to order this queue, or `null` if this queue is sorted according to 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 type of the specified element is incompatible with this collection (optional)
`java.lang.NullPointerException`	if the specified element is null and this collection does not permit null elements (optional)

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.

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.

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 this 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 this 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

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 type of the specified element is incompatible with this collection (optional)
`java.lang.NullPointerException`	if the specified element is null and this collection does not permit null elements (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

fun spliterator(): Spliterator<E>

Creates a late-binding and fail-fast Spliterator over the elements in this queue. The spliterator does not traverse elements in any particular order (the ORDERED characteristic is not reported).

The Spliterator reports Spliterator#SIZED, Spliterator#SUBSIZED, and Spliterator#NONNULL. Overriding implementations should document the reporting of additional characteristic values.

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

toArray

Added in API level 1

open fun toArray(): Array<Any!>

Returns an array containing all of the elements in this queue. The 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 the queue fits in the specified array with room to spare (i.e., the array has more elements than the queue), the element in the array immediately following the end of the collection 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

Properties

size

Added in API level 1

open val size: Int

Return
`Int`	the number of elements in this collection