Java ArrayBlockingQueue contains()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，你所存储的元素数量 不能 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进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。

contains(Object o) 方法 如果队列包含作为参数传递的对象o ，则返回true。我们可以说， 当且仅当 这个队列包含至少一个与作为参数传递的对象o相等的元素e，即o.equals(e)时，该方法返回真。

语法

public boolean contains(Object o)

参数：

o – 检查队列是否包含指定的对象。

返回值：

如果该队列包含该对象，则为true。

下面的程序说明了ArrayBlockingQueue的包含方法。

例1

// Java Program Demonstrate contains(Object o)
// 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 elements to ArrayBlockingQueue
        queue.add(23);
        queue.add(32);
        queue.add(45);
        queue.add(12);
  
        // check whether queue contains 23
        boolean response1 = queue.contains(23);
  
        // print after applying contains method with 23 as parameter
        System.out.println("queue contains 23 : " + response1);
  
        // check whether queue contains 99
        boolean response2 = queue.contains(99);
  
        // print after applying contains method with 99 as parameter
        System.out.println("queue contains 99 : " + response2);
    }
}

输出。

queue contains 23 : true
queue contains 99 : false

例2

// Java Program Demonstrate contains(Object o)
// method of ArrayBlockingQueue.
import java.util.concurrent.ArrayBlockingQueue;
  
public class GFG {
  
    // create a User Object with name and age as 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.containsMethodExample();
    }
  
    // Method to give example of contains function
    public void containsMethodExample()
    {
  
        // define capacity of ArrayBlockingQueue
        int capacity = 5;
  
        // create object of ArrayBlockingQueue
        ArrayBlockingQueue<User> queue
            = new ArrayBlockingQueue<User>(capacity);
  
        User user1 = new User("Aman", "24");
        User user2 = new User("Amar", "23");
        User user3 = new User("Sanjeet", "25");
        User user4 = new User("Suvo", "26");
  
        // Add Objects to ArrayBlockingQueue
        queue.add(user1);
        queue.add(user2);
        queue.add(user3);
        queue.add(user4);
  
        User user5 = new User("Ravi", "22");
        // check whether queue contains User1
        boolean response1 = queue.contains(user1);
  
        // print after applying contains method with user1 as parameter
        System.out.println("queue contains User having name "
                           + user1.name + " : " + response1);
  
        // check whether queue contains User5
        boolean response2 = queue.contains(user5);
  
        // print after applying contains method with user1 as parameter
        System.out.println("queue contains User having name "
                           + user5.name + " : " + response2);
    }
}

输出。

queue contains User having name Aman : true
queue contains User having name Ravi : false

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