ArrayBlockingQueue remainingCapacity() Method in Java

ArrayBlockingQueue is bounded, blocking queue that stores the elements internally backed by an array.

• ArrayBlockingQueue class is a member of the Java Collections Framework.
• Bounded means it will have a fixed size, you can not store number the elements more than the capacity of the queue.
• The queue also follows FIFO (first-in-first-out) rule for storing and removing elements from the queue.
• If you try to put an element into a full queue or to take an element from an empty queue then the queue will block you.

The remainingCapacity() method returns number of more elements that can be added to queue without blocking. This is always equal to difference between the initial capacity of this queue and the current size of this queue.

Syntax:

public int remainingCapacity()

Parameters: The method does not take any parameters.

Return Value: The method returns the remaining capacity of the queue.

Below programs illustrate remainingCapacity() method of ArrayBlockingQueue:
Program 1:

// Program to demonstrate remainingCapacity() 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);

        // Print queue after adding numbers
        System.out.println("Queue :" + queue);
        // Check remaining capacity
        int remainingCapacity = queue.remainingCapacity();
        System.out.println("Remaining Capacity:" +
                                       remainingCapacity);

        // Add elements to ArrayBlockingQueue
        queue.add(54);
        queue.add(78);

        // Print queue after adding numbers
        System.out.println("Queue :" + queue);
        // Check remaining capacity
        System.out.println("Remaining Capacity:" +
                               queue.remainingCapacity());
    }
}

Output:

Queue :[23, 32]
Remaining Capacity:3
Queue :[23, 32, 54, 78]
Remaining Capacity:1

Program 2:

// Program to demonstrate remainingCapacity() method
// of ArrayBlockingQueue

import java.util.concurrent.ArrayBlockingQueue;

public class GFG {
    // Create a User Object with name and age as an 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.RemainingCapacityExample();
    }
    // Method to give example of remaining capacity function
    public void RemainingCapacityExample()
    {

        // 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");

        // Add Objects to ArrayBlockingQueue
        queue.offer(user1);
        queue.offer(user2);
        queue.offer(user3);

        // Check remaining capacity
        int remainingCapacity = queue.remainingCapacity();
        System.out.println("Remaining Capacity:" +
                                       remainingCapacity);

        User user4 = new User("Suvo", "26");
        User user5 = new User("Ravi", "22");

        // Adding more objects
        queue.offer(user2);
        queue.offer(user3);

        // Check remaining capacity
        remainingCapacity = queue.remainingCapacity();
        System.out.println("Remaining Capacity:" +
                                     remainingCapacity);
    }
}

Output:

Remaining Capacity:2
Remaining Capacity:0

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