Java PriorityBlockingQueue peek()方法

PriorityBlockingQueue 的 peek() 方法返回PriorityBlockingQueue中 头部 的元素。它检索LinkedBlockingQueue的头部的值，但不删除它。如果PriorityBlockingQueue不包含任何元素，那么这个方法返回null。PriorityBlockingQueue队使用与PriorityQueue类相同的排序规则。

语法

public E peek()

参数： 该方法不接受任何参数。

返回： 该方法返回PriorityBlockingQueue的头部。

下面的程序说明了PriorityBlockingQueue的peek()方法。

例1 :

// Java Program Demonstrate peek()
// method of PriorityBlockingQueue
  
import java.util.concurrent.PriorityBlockingQueue;
  
public class GFG {
    public static void main(String[] args)
    {
        // define capacity of PriorityBlockingQueue
        int capacityOfQueue = 5;
  
        // create object of PriorityBlockingQueue
        PriorityBlockingQueue<Integer> PrioQueue
            = new PriorityBlockingQueue<Integer>(capacityOfQueue);
  
        // Add elements to PriorityBlockingQueue
        PrioQueue.add(464161);
        PrioQueue.add(416165);
  
        // print PrioQueue
        System.out.println("PrioQueue: " + PrioQueue);
  
        // get head of PriorityBlockingQueue
        int head = PrioQueue.peek();
  
        // print head of PriorityBlockingQueue
        System.out.println("Head of Queue: " + head);
    }
}

输出:

PrioQueue: [416165, 464161]
Head of Queue: 416165

例2： 说明PriorityBlockingQueue的peek()方法，该方法包含名字的列表。

// Java Program Demonstrate peek()
// method of PriorityBlockingQueue
  
import java.util.concurrent.PriorityBlockingQueue;
  
public class GFG {
    public static void main(String[] args)
    {
  
        // define capacity of PriorityBlockingQueue
        int capacityOfQueue = 5;
  
        // create object of PriorityBlockingQueue 
        PriorityBlockingQueue<String> names
            = new PriorityBlockingQueue<String>(capacityOfQueue);
  
        // Add names of students of girls college
        names.add("Geeks");
        names.add("forGeeks");
        names.add("A");
        names.add("Computer");
        names.add("Portal");
  
        // print PrioQueue
        System.out.println("List of Names: " + names.toString());
  
        // get head of PriorityBlockingQueue
        String head = names.peek();
  
        // print head of PriorityBlockingQueue
        System.out.println("Head of Queue: " + head);
  
        // remove one name from head
        names.poll();
        System.out.println("First Name from head is removed");
  
        // print PrioQueue
        System.out.println("List of Names: " + names.toString());
  
        // get head of PriorityBlockingQueue
        head = names.peek();
  
        // print head of PriorityBlockingQueue
        System.out.println("Head of Queue: " + head);
    }
}

输出:

List of Names: [A, Computer, Geeks, forGeeks, Portal]
Head of Queue: A
First Name from head is removed
List of Names: [Computer, Portal, Geeks, forGeeks]
Head of Queue: Computer

参考资料:
https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/PriorityBlockingQueue.html#peek-