MinMaxPriorityQueue (Guava: Google Core Libraries for Java 19.0 API)

java.lang.Object
- java.util.AbstractCollection<E>
- - java.util.AbstractQueue<E>
  - - com.google.common.collect.MinMaxPriorityQueue<E>

All Implemented Interfaces:

Iterable<E>, Collection<E>, Queue<E>
```
@Beta
public final class MinMaxPriorityQueue<E>
extends AbstractQueue<E>
```
A double-ended priority queue, which provides constant-time access to both its least element and its greatest element, as determined by the queue's specified comparator. If no comparator is given at creation time, the natural order of elements is used. If no maximum size is given at creation time, the queue is unbounded.
Usage example:
```
   MinMaxPriorityQueue<User> users = MinMaxPriorityQueue.orderedBy(userComparator)
       .maximumSize(1000)
       .create();
```
As a Queue it functions exactly as a PriorityQueue: its head element -- the implicit target of the methods peek(), poll() and AbstractQueue.remove() -- is defined as the least element in the queue according to the queue's comparator. But unlike a regular priority queue, the methods peekLast(), pollLast() and removeLast() are also provided, to act on the greatest element in the queue instead.
A min-max priority queue can be configured with a maximum size. If so, each time the size of the queue exceeds that value, the queue automatically removes its greatest element according to its comparator (which might be the element that was just added). This is different from conventional bounded queues, which either block or reject new elements when full.
This implementation is based on the min-max heap developed by Atkinson, et al. Unlike many other double-ended priority queues, it stores elements in a single array, as compact as the traditional heap data structure used in PriorityQueue.
This class is not thread-safe, and does not accept null elements.
Performance notes:
- If you only access one end of the queue, and do use a maximum size, this class will perform significantly worse than a PriorityQueue with manual eviction above the maximum size. In many cases Ordering.leastOf(java.lang.Iterable<E>, int) may work for your use case with significantly improved (and asymptotically superior) performance.
- The retrieval operations peek(), peekFirst(), peekLast(), AbstractQueue.element(), and size are constant-time.
- The enqueing and dequeing operations (offer(E), add(E), and all the forms of poll() and AbstractQueue.remove()) run in O(log n) time.
- The AbstractCollection.remove(Object) and AbstractCollection.contains(java.lang.Object) operations require linear (O(n)) time.
- If you only access one end of the queue, and don't use a maximum size, this class is functionally equivalent to PriorityQueue, but significantly slower.
Since:

8.0

Author:

Sverre Sundsdal, Torbjorn Gannholm

Nested Class Summary

Nested Classes
Modifier and Type Class and Description

static class MinMaxPriorityQueue.Builder<B>
The builder class used in creation of min-max priority queues.

Nested Classes
Modifier and Type	Class and Description
`static class`	`MinMaxPriorityQueue.Builder<B>` The builder class used in creation of min-max priority queues.

Method Summary

Methods
Modifier and Type	Method and Description
`boolean`	`add(E element)` Adds the given element to this queue.
`boolean`	`addAll(Collection<? extends E> newElements)`
`void`	`clear()`
`Comparator<? super E>`	`comparator()` Returns the comparator used to order the elements in this queue.
`static <E extends Comparable<E>> MinMaxPriorityQueue<E>`	`create()` Creates a new min-max priority queue with default settings: natural order, no maximum size, no initial contents, and an initial expected size of 11.
`static <E extends Comparable<E>> MinMaxPriorityQueue<E>`	`create(Iterable<? extends E> initialContents)` Creates a new min-max priority queue using natural order, no maximum size, and initially containing the given elements.
`static MinMaxPriorityQueue.Builder<Comparable>`	`expectedSize(int expectedSize)` Creates and returns a new builder, configured to build `MinMaxPriorityQueue` instances sized appropriately to hold `expectedSize` elements.
`Iterator<E>`	`iterator()` Returns an iterator over the elements contained in this collection, in no particular order.
`static MinMaxPriorityQueue.Builder<Comparable>`	`maximumSize(int maximumSize)` Creates and returns a new builder, configured to build `MinMaxPriorityQueue` instances that are limited to `maximumSize` elements.
`boolean`	`offer(E element)` Adds the given element to this queue.
`static <B> MinMaxPriorityQueue.Builder<B>`	`orderedBy(Comparator<B> comparator)` Creates and returns a new builder, configured to build `MinMaxPriorityQueue` instances that use `comparator` to determine the least and greatest elements.
`E`	`peek()`
`E`	`peekFirst()` Retrieves, but does not remove, the least element of this queue, or returns `null` if the queue is empty.
`E`	`peekLast()` Retrieves, but does not remove, the greatest element of this queue, or returns `null` if the queue is empty.
`E`	`poll()`
`E`	`pollFirst()` Removes and returns the least element of this queue, or returns `null` if the queue is empty.
`E`	`pollLast()` Removes and returns the greatest element of this queue, or returns `null` if the queue is empty.
`E`	`removeFirst()` Removes and returns the least element of this queue.
`E`	`removeLast()` Removes and returns the greatest element of this queue.
`int`	`size()`
`Object[]`	`toArray()`

Methods inherited from class java.util.AbstractQueue
element, remove

Methods inherited from class java.util.AbstractCollection
contains, containsAll, isEmpty, remove, removeAll, retainAll, toArray, toString

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.util.Collection
contains, containsAll, equals, hashCode, isEmpty, remove, removeAll, retainAll, toArray

- Method Detail
  - create
```
public static <E extends Comparable<E>> MinMaxPriorityQueue<E> create()
```
    Creates a new min-max priority queue with default settings: natural order, no maximum size, no initial contents, and an initial expected size of 11.
  - create
```
public static <E extends Comparable<E>> MinMaxPriorityQueue<E> create(Iterable<? extends E> initialContents)
```
    Creates a new min-max priority queue using natural order, no maximum size, and initially containing the given elements.
  - orderedBy
```
public static <B> MinMaxPriorityQueue.Builder<B> orderedBy(Comparator<B> comparator)
```
    Creates and returns a new builder, configured to build MinMaxPriorityQueue instances that use comparator to determine the least and greatest elements.
  - expectedSize
```
public static MinMaxPriorityQueue.Builder<Comparable> expectedSize(int expectedSize)
```
    Creates and returns a new builder, configured to build MinMaxPriorityQueue instances sized appropriately to hold expectedSize elements.
  - maximumSize
```
public static MinMaxPriorityQueue.Builder<Comparable> maximumSize(int maximumSize)
```
    Creates and returns a new builder, configured to build MinMaxPriorityQueue instances that are limited to maximumSize elements. Each time a queue grows beyond this bound, it immediately removes its greatest element (according to its comparator), which might be the element that was just added.
  - size
```
public int size()
```
    Specified by:
    
    size in interface Collection<E>
    
    Specified by:
    
    size in class AbstractCollection<E>
  - add
```
public boolean add(E element)
```
    Adds the given element to this queue. If this queue has a maximum size, after adding element the queue will automatically evict its greatest element (according to its comparator), which may be element itself.
    
    Specified by:
    
    add in interface Collection<E>
    
    Specified by:
    
    add in interface Queue<E>
    
    Overrides:
    
    add in class AbstractQueue<E>
    
    Returns:
    true always
  - addAll
```
public boolean addAll(Collection<? extends E> newElements)
```
    Specified by:
    
    addAll in interface Collection<E>
    
    Overrides:
    
    addAll in class AbstractQueue<E>
  - offer
```
public boolean offer(E element)
```
    Adds the given element to this queue. If this queue has a maximum size, after adding element the queue will automatically evict its greatest element (according to its comparator), which may be element itself.
  - poll
```
public E poll()
```
  - peek
```
public E peek()
```
  - pollFirst
```
public E pollFirst()
```
    Removes and returns the least element of this queue, or returns null if the queue is empty.
  - removeFirst
```
public E removeFirst()
```
    Removes and returns the least element of this queue.
    
    Throws:
    
    NoSuchElementException - if the queue is empty
  - peekFirst
```
public E peekFirst()
```
    Retrieves, but does not remove, the least element of this queue, or returns null if the queue is empty.
  - pollLast
```
public E pollLast()
```
    Removes and returns the greatest element of this queue, or returns null if the queue is empty.
  - removeLast
```
public E removeLast()
```
    Removes and returns the greatest element of this queue.
    
    Throws:
    
    NoSuchElementException - if the queue is empty
  - peekLast
```
public E peekLast()
```
    Retrieves, but does not remove, the greatest element of this queue, or returns null if the queue is empty.
  - iterator
```
public Iterator<E> iterator()
```
    Returns an iterator over the elements contained in this collection, in no particular order.
    The iterator is fail-fast: If the MinMaxPriorityQueue is modified at any time after the iterator is created, in any way except through the iterator's own remove method, the iterator will generally throw a ConcurrentModificationException. Thus, in the face of concurrent modification, the iterator fails quickly and cleanly, rather than risking arbitrary, non-deterministic behavior at an undetermined time in the future.
    Note that the fail-fast behavior of an iterator cannot be guaranteed as it is, generally speaking, impossible to make any hard guarantees in the presence of unsynchronized concurrent modification. Fail-fast iterators throw ConcurrentModificationException on a best-effort basis. Therefore, it would be wrong to write a program that depended on this exception for its correctness: the fail-fast behavior of iterators should be used only to detect bugs.
    
    Specified by:
    
    iterator in interface Iterable<E>
    
    Specified by:
    
    iterator in interface Collection<E>
    
    Specified by:
    
    iterator in class AbstractCollection<E>
    
    Returns:
    an iterator over the elements contained in this collection
  - clear
```
public void clear()
```
    Specified by:
    
    clear in interface Collection<E>
    
    Overrides:
    
    clear in class AbstractQueue<E>
  - toArray
```
public Object[] toArray()
```
    Specified by:
    
    toArray in interface Collection<E>
    
    Overrides:
    
    toArray in class AbstractCollection<E>
  - comparator
```
public Comparator<? super E> comparator()
```
    Returns the comparator used to order the elements in this queue. Obeys the general contract of PriorityQueue.comparator, but returns Ordering.natural() instead of null to indicate natural ordering.

Class MinMaxPriorityQueue<E>

Nested Class Summary

Method Summary

Methods inherited from class java.util.AbstractQueue

Methods inherited from class java.util.AbstractCollection

Methods inherited from class java.lang.Object

Methods inherited from interface java.util.Collection

Method Detail

create

create

orderedBy

expectedSize

maximumSize

size

add

addAll

offer

poll

peek

pollFirst

removeFirst

peekFirst

pollLast

removeLast

peekLast

iterator

clear

toArray

comparator