Java中的 ArrayBlockingQueue peek() 方法

ArrayBlockingQueue是有界的阻塞队列，它在内部存储由数组支持的元素。

• ArrayBlockingQueue类是Java集合框架的成员。
• 有界意味着它将具有固定大小，您不能存储数量超过队列容量的元素。
• 队列还遵循 FIFO（先进先出）规则来存储和删除队列中的元素。
• 如果你试图将一个元素放入一个满队列或从一个空队列中取出一个元素，那么队列会阻止你。

peek()方法用于返回队列的头部。它检索但不删除此队列的头部。如果队列为空，则此方法返回 null。
句法：

public E peek()

参数：该方法不带任何参数。
返回值：该方法返回此队列头部的元素。
下面的程序说明了 ArrayBlockingQueue 的 peek() 方法。
方案一：

Java

// 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 queue =
         new ArrayBlockingQueue(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 adding numbers queue is ");
    System.out.println(queue);
 
    // Print head of queue using peek() method
    System.out.println("Head of queue "+queue.peek());
     
}
}

输出：

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

方案二：

Java

// 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 queue =
                new ArrayBlockingQueue(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);
    }
}

输出：

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

参考： https: Java/util/concurrent/ArrayBlockingQueue.html#peek()