Java中的PriorityQueue poll() 方法
Java中的Java .util.PriorityQueue.poll() 方法用于检索或获取和删除队列的第一个元素或存在于队列头部的元素。 peek() 方法仅检索头部的元素,但 poll() 也会在检索时删除该元素。如果队列为空,则返回 NULL。
句法:
Priority_Queue.poll()
参数:该方法不带任何参数。
返回值:该方法返回队列头部的元素,如果队列为空,则返回NULL。
下面的程序说明了Java.util.PriorityQueue.poll() 方法的使用:
方案一:
// Java code to illustrate poll()
import java.util.*;
public class PriorityQueueDemo {
public static void main(String args[])
{
// Creating an empty PriorityQueue
PriorityQueue queue = new PriorityQueue();
// Use add() method to add elements into the Queue
queue.add("Welcome");
queue.add("To");
queue.add("Geeks");
queue.add("For");
queue.add("Geeks");
// Displaying the PriorityQueue
System.out.println("Initial PriorityQueue: " + queue);
// Fetching and removing the element at the head of the queue
System.out.println("The element at the head of the"
+ " queue is: " + queue.poll());
// Displaying the Queue after the Operation
System.out.println("Final PriorityQueue: " + queue);
}
}
输出:
Initial PriorityQueue: [For, Geeks, To, Welcome, Geeks]
The element at the head of the queue is: For
Final PriorityQueue: [Geeks, Geeks, To, Welcome]
方案二:
// Java code to illustrate poll()
import java.util.*;
public class PriorityQueueDemo {
public static void main(String args[])
{
// Creating an empty PriorityQueue
PriorityQueue queue = new PriorityQueue();
// Use add() method to add elements into the Queue
queue.add(10);
queue.add(15);
queue.add(30);
queue.add(20);
queue.add(5);
// Displaying the PriorityQueue
System.out.println("Initial PriorityQueue: " + queue);
// Fetching the element at the head of the queue
System.out.println("The element at the head of the"
+ " queue is: " + queue.poll());
// Displaying the Queue after the Operation
System.out.println("Final PriorityQueue: " + queue);
}
}
输出:
Initial PriorityQueue: [5, 10, 30, 20, 15]
The element at the head of the queue is: 5
Final PriorityQueue: [10, 15, 30, 20]