java-PriorityQueue优先队列

当应该基于优先级处理对象时，使用PriorityQueue。众所周知，队列遵循先进先出算法，但有时需要根据优先级处理队列的元素，即当PriorityQueue发挥作用时。 PriorityQueue基于优先级堆。优先级队列的元素按照自然顺序排序，或者由队列构造时提供的比较器排序，具体取决于使用的构造函数。

通过下面的demo来简单的介绍一下的java的 PriorityQueue

// Java progrm to demonstrate working of priority queue in Java 
import java.util.*; 

class Example 
{ 
	public static void main(String args[]) 
	{ 
		// Creating empty priority queue 
		PriorityQueue<String> pQueue = 
						new PriorityQueue<String>(); 

		// Adding items to the pQueue using add() 
		pQueue.add("C"); 
		pQueue.add("C++"); 
		pQueue.add("Java"); 
		pQueue.add("Python"); 

		// Printing the most priority element 
		System.out.println("Head value using peek function:"
										+ pQueue.peek()); 

		// Printing all elements 
		System.out.println("The queue elements:"); 
		Iterator itr = pQueue.iterator(); 
		while (itr.hasNext()) 
			System.out.println(itr.next()); 

		// Removing the top priority element (or head) and 
		// printing the modified pQueue using poll() 
		pQueue.poll(); 
		System.out.println("After removing an element" + 
						"with poll function:"); 
		Iterator<String> itr2 = pQueue.iterator(); 
		while (itr2.hasNext()) 
			System.out.println(itr2.next()); 

		// Removing Java using remove() 
		pQueue.remove("Java"); 
		System.out.println("after removing Java with" + 
						" remove function:"); 
		Iterator<String> itr3 = pQueue.iterator(); 
		while (itr3.hasNext()) 
			System.out.println(itr3.next()); 

		// Check if an element is present using contains() 
		boolean b = pQueue.contains("C"); 
		System.out.println ( "Priority queue contains C " + 
							"or not?: " + b); 

		// Getting objects from the queue using toArray() 
		// in an array and print the array 
		Object[] arr = pQueue.toArray(); 
		System.out.println ( "Value in array: "); 
		for (int i = 0; i<arr.length; i++) 
		System.out.println ( "Value: " + arr[i].toString()) ; 
	} 
}

运行结果如下

➜  queue git:(master) ✗ java Example
Head value using peek function:C
The queue elements:
C
C++
Java
Python
After removing an elementwith poll function:
C++
Python
Java
after removing Java with remove function:
C++
Python
Priority queue contains C or not?: false
Value in array:
Value: C++
Value: Python

boolean add(E element): This method inserts the specified element into this priority queue.
public remove(): This method removes a single instance of the specified element from this queue, if it is present
public poll(): This method retrieves and removes the head of this queue, or returns null if this queue is empty.
public peek(): This method retrieves, but does not remove, the head of this queue, or returns null if this queue is empty.
Iterator iterator(): Returns an iterator over the elements in this queue.
boolean contains(Object o): This method returns true if this queue contains the specified element
void clear(): This method is used to remove all of the contents of the priority queue.
boolean offer(E e): This method is used to insert a specific element into the priority queue.
int size(): The method is used to return the number of elements present in the set.
toArray(): This method is used to return an array containing all of the elements in this queue.
Comparator comparator(): The method is used to return the comparator that can be used to order the elements of the queue.

java-PriorityQueue优先队列

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