Java ConcurrentLinkedQueue peek()用法及代碼示例

ConcurrentLinkedQueue的peek()方法用於返回ConcurrentLinkedQueue的頭。它檢索但不刪除此ConcurrentLinkedQueue的頭部。如果ConcurrentLinkedQueue為空，則此方法返回null。

用法:

public E peek()

返回值：此方法返回此ConcurrentLinkedQueue的頭部，而不刪除它。

以下示例程序旨在說明ConcurrentLinkedQueue的peek()方法：

示例1:

// Java Program Demonstrate peek() 
// method of ConcurrentLinkedQueue 
  
import java.util.concurrent.*; 
  
public class GFG { 
    public static void main(String[] args) 
    { 
  
        // create an ConcurrentLinkedQueue 
        ConcurrentLinkedQueue<Integer> 
            queue = new ConcurrentLinkedQueue<Integer>(); 
  
        // Add Numbers to queue 
        queue.add(4353); 
        queue.add(7824); 
        queue.add(78249); 
        queue.add(8724); 
  
        // Displaying the existing ConcurrentLinkedQueue 
        System.out.println("ConcurrentLinkedQueue: " + queue); 
  
        // find peek 
        int response1 = queue.peek(); 
  
        // print after applying peek method 
        System.out.println("Head: " + response1); 
  
        // Verifying that the head is not removed 
        System.out.println("ConcurrentLinkedQueue after peek: " + queue); 
    } 
}

輸出：

ConcurrentLinkedQueue: [4353, 7824, 78249, 8724]
Head: 4353
ConcurrentLinkedQueue after peek: [4353, 7824, 78249, 8724]

示例2:

// Java Program Demonstrate peek() 
// method of ConcurrentLinkedQueue 
  
import java.util.concurrent.*; 
  
public class GFG { 
    public static void main(String[] args) 
    { 
  
        // create an ConcurrentLinkedQueue 
        ConcurrentLinkedQueue<String> 
            queue = new ConcurrentLinkedQueue<String>(); 
  
        // Add String to queue 
        queue.add("Aman"); 
        queue.add("Amar"); 
        queue.add("Sanjeet"); 
        queue.add("Rabi"); 
  
        // Displaying the existing ConcurrentLinkedQueue 
        System.out.println("ConcurrentLinkedQueue: " + queue); 
  
        // find peek of queue 
        String response1 = queue.peek(); 
  
        // print after applying peek method 
        System.out.println("Head: " + response1); 
  
        // Verifying that the head is not removed 
        System.out.println("ConcurrentLinkedQueue after peek: " + queue); 
  
        // remove some elements 
        queue.poll(); 
        queue.poll(); 
  
        // Displaying the existing ConcurrentLinkedQueue 
        System.out.println("Updated ConcurrentLinkedQueue: " + queue); 
  
        // find peek of queue 
        String response2 = queue.peek(); 
  
        // print after applying peek method 
        System.out.println("Head: " + response1); 
  
        // Verifying that the head is not removed 
        System.out.println("ConcurrentLinkedQueue after peek: " + queue); 
    } 
}

輸出：

ConcurrentLinkedQueue: [Aman, Amar, Sanjeet, Rabi]

Head: Aman

ConcurrentLinkedQueue after peek: [Aman, Amar, Sanjeet, Rabi]

Updated ConcurrentLinkedQueue: [Sanjeet, Rabi]

Head: Aman

ConcurrentLinkedQueue after peek: [Sanjeet, Rabi]

參考： https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ConcurrentLinkedQueue.html#peek–

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