Java中的 PriorityQueue peek() 方法

Java中的Java .util.PriorityQueue.peek() 方法用于检索或获取队列的第一个元素或队列头部的元素。检索到的元素不会从队列中删除或移除。

句法：

Priority_Queue.peek()

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.peek() 方法：
方案一：

// Java code to illustrate peek()
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 the element at the head of the queue
        System.out.println("The element at the head of the"
                           + " queue is: " + queue.peek());
  
        // 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: [For, Geeks, To, Welcome, Geeks]

方案二：

// Java code to illustrate peek()
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.peek());
  
        // 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: [5, 10, 30, 20, 15]