Java ArrayBlockingQueue peek()用法及代碼示例

ArrayBlockingQueue是有界的阻塞隊列，該隊列內部使用數組支持的元素存儲。

ArrayBlockingQueue類是Java Collections Framework的成員。
有界意味著它將具有固定的大小，您不能存儲數量超過隊列容量的元素。
隊列還遵循FIFO(先進先出)規則，用於存儲和刪除隊列中的元素。
如果您嘗試將一個元素放入一個完整的隊列或從一個空隊列中取出一個元素，那麽該隊列將阻塞。

peek()方法用於返回隊列的頭部。它檢索但不刪除此隊列的頭。如果隊列為空，則此方法返回null。

用法:

public E peek()

參量：該方法不帶任何參數。

返回值：該方法返回存在於此隊列開頭的元素。

下麵的程序說明ArrayBlockingQueue的peek()方法。
示例1:

// Program to demonstrate peek() method of ArrayBlockingQueue 
  
import java.util.concurrent.ArrayBlockingQueue; 
  
public class GFG { 
  
public static void main(String[] args) { 
    // Define capacity of ArrayBlockingQueue 
    int capacity = 5; 
      
    // Create object of ArrayBlockingQueue 
    ArrayBlockingQueue<Integer> queue =  
         new ArrayBlockingQueue<Integer>(capacity); 
      
    // Add element to ArrayBlockingQueue 
    queue.add(23); 
    queue.add(32); 
    queue.add(45); 
    queue.add(12); 
      
    // Print queue after adding numbers 
    System.out.println("After addding numbers queue is "); 
    System.out.println(queue); 
  
    // Print head of queue using peek() method 
    System.out.println("Head of queue "+queue.peek()); 
      
}  
}

輸出：

After addding numbers queue is 
[23, 32, 45, 12]
Head of queue 23

示例2:

// Program to demonstrate contains(Object o) method of ArrayBlockingQueue 
  
import java.util.concurrent.ArrayBlockingQueue; 
  
public class GFG { 
      
    // Create a User Object with name and age as the attribute 
    public class User{ 
          
        public String name; 
        public String age; 
        User(String name,String age){ 
            this.name=name; 
            this.age=age; 
        } 
          
    } 
      
    // Main Method 
    public static void main(String[] args) { 
        GFG gfg=new GFG(); 
        gfg.offerExample(); 
          
    }  
      
    // Method to give example of contains function 
    public void offerExample() { 
          
        // Define capacity of ArrayBlockingQueue 
            int capacity = 5; 
              
            // Create object of ArrayBlockingQueue 
            ArrayBlockingQueue<User> queue = 
                new ArrayBlockingQueue<User>(capacity); 
              
            // Create user objects 
            User user1=new User("Aman","24"); 
            User user2=new User("Amar","23"); 
            User user3=new User("Sanjeet","25"); 
            User user4=new User("Suvo","26"); 
            User user5=new User("Ravi","22");  
              
            // Add Objects to ArrayBlockingQueue 
            queue.offer(user1); 
            queue.offer(user2); 
            queue.offer(user3); 
            queue.offer(user4); 
            queue.offer(user5); 
              
            // Find peek of queue 
           User head=queue.peek(); 
            
            // Print head 
            System.out.println("Details of First User Inserted"); 
            System.out.println("User Name : "+head.name); 
            System.out.println("User Age : "+head.age); 
    } 
}

輸出：

Details of First User Inserted
User Name : Aman
User Age : 24

參考： https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/ArrayBlockingQueue.html#peek()

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注：本文由純淨天空篩選整理自AmanSingh2210大神的英文原創作品 ArrayBlockingQueue peek() Method in Java。非經特殊聲明，原始代碼版權歸原作者所有，本譯文未經允許或授權，請勿轉載或複製。