Java ArrayBlockingQueue peek()方法

ArrayBlockingQueue 是有边界的、阻塞的队列，它在内部存储了由数组支持的元素。

• ArrayBlockingQueue 类是Java集合框架的一个成员。
• 有界意味着它将有一个固定的大小，你不能存储的元素数量超过队列的容量。
• 该队列也遵循FIFO（先进先出）规则来存储和移除队列中的元素。
• 如果你试图把一个元素放入一个满的队列或从一个空的队列中取出一个元素，那么队列将阻止你。

peek() 方法用于返回队列的头部。它检索但不删除这个队列的头部。如果队列是空的，那么这个方法返回null。

语法：

public E peek()

参数 ：该方法不接受任何参数。

返回值： 该方法返回该队列头部的元素。

以下程序说明了ArrayBlockingQueue的peek()方法。

程序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 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 adding 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);
    }
}

输出

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

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