PriorityQueue

All Known Implementing Classes:

ArrayPriorityQueue
```
public interface PriorityQueue<Element extends java.lang.Comparable>
```
A PriorityQueue represents an unbounded queue of items arranged in some priority order. This queue orders items according to their natural order (see Comparable). A priority queue does not permit null elements. A priority queue also does not permit insertion of non-comparable objects (doing so may result in ClassCastException).
The head of this queue is the greatest element with respect to the specified ordering. If multiple elements are tied for greatest value, the head is one of those elements -- ties are broken arbitrarily. The queue retrieval operations dequeue and peek access the element at the head of the queue.

Method Summary

Methods
Modifier and Type	Method and Description
`void`	`clear()` Removes all elements from the priority queue.
`Element`	`dequeue()` Retrieves and removes the head of this queue.
`void`	`enqueue(Element element)` Adds the specified element to this priority queue.
`boolean`	`isEmpty()` Indicates whether or not the queue is empty.
`Element`	`peek()` Retrieves, but does not remove, the head of this queue.
`int`	`size()` Returns the number of elements currently in this queue.

- Method Detail
  - clear
```
void clear()
```
    Removes all elements from the priority queue.
  - peek
```
Element peek()
```
    Retrieves, but does not remove, the head of this queue.
    
    Returns:
    the head item in the queue, or null if this queue is empty.
  - dequeue
```
Element dequeue()
```
    Retrieves and removes the head of this queue.
    
    Returns:
    the head item in the queue, or null if this queue is empty.
  - enqueue
```
void enqueue(Element element)
```
    Adds the specified element to this priority queue.
    
    Parameters:
    element - is an item to be enqueued
  - size
```
int size()
```
    Returns the number of elements currently in this queue.
    
    Returns:
    int the size of the queue
  - isEmpty
```
boolean isEmpty()
```
    Indicates whether or not the queue is empty.
    
    Returns:
    true if the queue size is zero, false otherwise.