Class PriorityQueue<E>

java.lang.Object
java.util.AbstractCollection<E>
java.util.AbstractQueue<E>
java.util.PriorityQueue<E>
All Implemented Interfaces:
Iterable<E>, Collection<E>, Queue<E>
public class PriorityQueue<E> extends AbstractQueue<E>

A PriorityQueue holds elements on a priority heap, which orders the elements according to their natural order or according to the comparator specified at construction time. If the queue uses natural ordering, only elements that are comparable are permitted to be inserted into the queue.

The least element of the specified ordering is stored at the head of the queue and the greatest element is stored at the tail of the queue.

A PriorityQueue is not synchronized. If multiple threads will have to access it concurrently, use the java.util.concurrent.PriorityBlockingQueue.

  • Constructor Details

    • PriorityQueue

      public PriorityQueue()
      Constructs a priority queue with an initial capacity of 11 and natural ordering.

    • PriorityQueue

      public PriorityQueue(int initialCapacity)

      Constructs a priority queue with the specified capacity and natural ordering.

      Parameters
      • initialCapacity: the specified capacity.
      Throws
      • IllegalArgumentException: if the initialCapacity is less than 1.

    • PriorityQueue

      public PriorityQueue(int initialCapacity, Comparator<? super E> comparator)

      Constructs a priority queue with the specified capacity and comparator.

      Parameters

      • initialCapacity: the specified capacity.

      • comparator: @param comparator the specified comparator. If it is null, the natural ordering will be used.

      Throws
      • IllegalArgumentException: if the initialCapacity is less than 1.

    • PriorityQueue

      public PriorityQueue(Collection<? extends E> c)

      Constructs a priority queue that contains the elements of a collection. The constructed priority queue has the initial capacity of 110% of the size of the collection. The queue uses natural ordering to order its elements.

      Parameters
      • c: @param c the collection whose elements will be added to the priority queue to be constructed.
      Throws

      • ClassCastException: if any of the elements in the collection are not comparable.

      • NullPointerException: if any of the elements in the collection are null.

    • PriorityQueue

      public PriorityQueue(PriorityQueue<? extends E> c)

      Constructs a priority queue that contains the elements of another priority queue. The constructed priority queue has the initial capacity of 110% of the specified one. Both priority queues have the same comparator.

      Parameters
      • c: @param c the priority queue whose elements will be added to the priority queue to be constructed.

    • PriorityQueue

      public PriorityQueue(SortedSet<? extends E> c)

      Constructs a priority queue that contains the elements of a sorted set. The constructed priority queue has the initial capacity of 110% of the size of the sorted set. The priority queue will have the same comparator as the sorted set.

      Parameters
      • c: @param c the sorted set whose elements will be added to the priority queue to be constructed.

  • Method Details

    • iterator

      public Iterator<E> iterator()

      Gets the iterator of the priority queue, which will not return elements in any specified ordering.

      Returns

      the iterator of the priority queue.

      Specified by:
      iterator in interface Collection<E>
      Specified by:
      iterator in interface Iterable<E>
      Specified by:
      iterator in class AbstractCollection<E>

    • size

      public int size()

      Gets the size of the priority queue. If the size of the queue is greater than the Integer.MAX, then it returns Integer.MAX.

      Returns

      the size of the priority queue.

      Specified by:
      size in interface Collection<E>
      Specified by:
      size in class AbstractCollection<E>
      Returns:
      how many objects this Collection contains, or Integer.MAX_VALUE if there are more than Integer.MAX_VALUE elements in this Collection.

    • clear

      public void clear()
      Removes all the elements of the priority queue.
      Specified by:
      clear in interface Collection<E>
      Overrides:
      clear in class AbstractQueue<E>

    • offer

      public boolean offer(E o)

      Inserts the element to the priority queue.

      Parameters
      • o: the element to add to the priority queue.
      Returns

      always true

      Throws

      • ClassCastException: @throws ClassCastException if the element cannot be compared with the elements in the priority queue using the ordering of the priority queue.

      • NullPointerException: if o is null.

      Returns:
      true if the operation succeeds and false if it fails.

    • poll

      public E poll()

      Gets and removes the head of the queue.

      Returns

      the head of the queue or null if the queue is empty.

      Returns:
      the element at the head of the queue or null if there is no element in the queue.

    • peek

      public E peek()

      Gets but does not remove the head of the queue.

      Returns

      the head of the queue or null if the queue is empty.

      Returns:
      the element at the head of the queue or null if there is no element in the queue.

    • comparator

      public Comparator<? super E> comparator()

      Gets the comparator of the priority queue.

      Returns
      Returns:
      the comparator of the priority queue or null if the natural ordering is used.

    • remove

      public boolean remove(Object o)

      Removes the specified object from the priority queue.

      Parameters
      • o: the object to be removed.
      Returns
      Specified by:
      remove in interface Collection<E>
      Overrides:
      remove in class AbstractCollection<E>
      Returns:
      true if the object was in the priority queue, false if the object was not in the priority queue.

    • add

      public boolean add(E o)

      Adds the specified object to the priority queue.

      Parameters
      • o: the object to be added.
      Returns

      always true.

      Throws

      • ClassCastException: @throws ClassCastException if the element cannot be compared with the elements in the priority queue using the ordering of the priority queue.

      • NullPointerException: if o is null.

      Specified by:
      add in interface Collection<E>
      Overrides:
      add in class AbstractQueue<E>
      Returns:

      true if this Collection is modified, false otherwise.

      Throws

      • UnsupportedOperationException: if adding to this Collection is not supported.

      • ClassCastException: @throws ClassCastException if the class of the object is inappropriate for this collection.

      • IllegalArgumentException: if the object cannot be added to this Collection.

      • NullPointerException: if null elements cannot be added to the Collection.

    • contains

      public boolean contains(Object object)

      Answers if there is an element in this queue equals to the object.

      See also
      • java.util.AbstractCollection#contains(java.lang.Object)
      Specified by:
      contains in interface Collection<E>
      Overrides:
      contains in class AbstractCollection<E>
      Returns:

      true if object is an element of this Collection, false otherwise.

      Throws

      • ClassCastException: @throws ClassCastException if the object to look for isn't of the correct type.

      • NullPointerException: @throws NullPointerException if the object to look for is null and this Collection doesn't support null elements.

    • toArray

      public Object[] toArray()

      Returns all the elements in an array. The result is a copy of all the elements.

      Returns

      the Array of all the elements

      See also
      • java.util.AbstractCollection#toArray()
      Specified by:
      toArray in interface Collection<E>
      Overrides:
      toArray in class AbstractCollection<E>

    • toArray

      public <T> T[] toArray(T[] array)
      Returns all the elements in an array, and the type of the result array is the type of the argument array. If the argument array is big enough, the elements from the queue will be stored in it(element immediately following the end of the queue is set to null, if any); otherwise, it will return a new array with the size of the argument array and size of the queue.
      Specified by:
      toArray in interface Collection<E>
      Overrides:
      toArray in class AbstractCollection<E>
      Parameters:
      the -

      type of elements in the array

      Parameters
      • array: @param array the array stores all the elements from the queue, if it has enough space; otherwise, a new array of the same type and the size of the queue will be used
      Returns

      the Array of all the elements

      Throws

      • ArrayStoreException: @throws ArrayStoreException if the type of the argument array is not compatible with every element in the queue

      • NullPointerException: if the argument array is null

      See also
      • java.util.AbstractCollection#toArray(T[])