ArrayBlockingQueue offer() 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.

There are two types of offer() method depending upon parameter passed to it:

1. The offer(E element) method inserts the element passed as parameter to method at the tail of this queue(ArrayBlockingQueue), if queue is not full. It returns true when the operation of addition is successful and false if this queue is full. This method is preferred over add() method because add method throws error when queue is full but offer() method returns false in such situation.
   Syntax:

   public boolean offer(E e)

   Parameter: The method takes one parameter, element. This refers to the element to be added in the queue.

   Return Value: This method returns True when the addition operation is successful and false if this queue is full.

   Exception The method throws NullPointerException if the specified element is null.

   Below programs illustrate offer(E element) method of ArrayBlockingQueue:
   Program 1:

   // Demonstrating offer(E element) 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 5 elements to ArrayBlockingQueue
       System.out.println("adding 423: "+queue.offer(423));
       System.out.println("adding 243: "+queue.offer(243));
       System.out.println("adding 237: "+queue.offer(237));
       System.out.println("adding 867: "+queue.offer(867));
       System.out.println("adding 23: "+queue.offer(23));
   
       // Check whether queue is full or not
       if(queue.remainingCapacity()==0) {
           System.out.println("queue is full");
           System.out.println("queue contains "+queue);
       }else {
           System.out.println("queue is not full");
           System.out.println("queue contains "+queue);
       }
   
       // Try to add more elements
       System.out.println("adding 123: "+queue.offer(123));
       System.out.println("adding 321: "+queue.offer(321));
   
   }
   }
   Output:

   adding 423: true
   adding 243: true
   adding 237: true
   adding 867: true
   adding 23: true
   queue is full
   queue contains [423, 243, 237, 867, 23]
   adding 123: false
   adding 321: false
   

   Program 2:

   // Program Demonstrate offer(E e) 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.offerExample();
       }
   
       // Method to give example of offer function
       public void offerExample()
       {
   
           // Define the 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
           System.out.println("adding user having name = "
                   + user1.name + ": " + queue.offer(user1));
           System.out.println("adding user having name = "
                   + user2.name + ": " + queue.offer(user2));
           System.out.println("adding user having name = "
                   + user3.name + ": " + queue.offer(user3));
           System.out.println("adding user having name = "
                   + user4.name + ": " + queue.offer(user4));
           System.out.println("adding user having name = "
                   + user5.name + ": " + queue.offer(user5));
   
           // Check whether the queue is full or not
           if (queue.remainingCapacity() == 0) {
               System.out.println("queue is full");
           }
           else {
               System.out.println("queue is not full");
           }
   
           // Create more user objects
           User user6 = new User("Ram", "20");
           User user7 = new User("Mohan", "27");
   
           // Add users in queue
           System.out.println("adding user having name = "
                   + user6.name + ": " + queue.offer(user6));
           System.out.println("adding user having name = "
                   + user7.name + ": " + queue.offer(user7));
       }
   }
   Output:

   adding user having name = Aman: true
   adding user having name = Amar: true
   adding user having name = Sanjeet: true
   adding user having name = Suvo: true
   adding user having name = Ravi: true
   queue is full
   adding user having name = Ram: false
   adding user having name = Mohan: false
   

2. The offer(E element, long timeout, TimeUnit unit) method inserts the element passed as parameter to method at the tail of this queue(ArrayBlockingQueue) if queue is not full. It will wait till a specified time for space to become available if the queue is full. It returns true when the operation of addition is successful and false if this queue is full and the specified waiting time elapses before space is available. This method is useful when we want to wait for the queue to remove its element and when the queue is not full the element will be added to the queue but we can wait for a specific time and this time can be defined by us.

   Syntax:

   public boolean offer(E e, long timeout, TimeUnit unit) throws InterruptedException

   Parameter: The method takes three parameters:

   • element (Object)- the element to add in the queue.
   • timeout (long)- how long to wait before giving up, in units of the unit.
   • unit (TimeUnit)- a TimeUnit determining how to interpret the timeout parameter.

   Return Value: The method returns True when adding method is successful and false if the specified waiting time elapses before space is available.

   Exception: The method throws two type of exceptions:

   • InterruptedException – if interrupted while waiting.
   • NullPointerException – if the specified element is null.

   Below programs illustrate the offer(E element, long timeout, TimeUnit unit)method of ArrayBlockingQueue:

   // Program Demonstrate offer(E e, long timeout, TimeUnit unit)
   // method of ArrayBlockingQueue
   
   import java.util.concurrent.ArrayBlockingQueue;
   import java.util.concurrent.TimeUnit;
   
   public class GFG {
   
       public static void main(String[] args)
                     throws InterruptedException
       {
           // Define capacity of ArrayBlockingQueue
           int capacity = 5;
   
           // Create object of ArrayBlockingQueue
           ArrayBlockingQueue<Integer> queue =
               new ArrayBlockingQueue<Integer>(capacity);
   
           // Add 5 elements to ArrayBlockingQueue having
           // Timeout in seconds with value 10 secs
           System.out.println("adding 423: " +
                 queue.offer(433, 10, TimeUnit.SECONDS));
           System.out.println("adding 456: " +
                 queue.offer(456, 10, TimeUnit.SECONDS));
           System.out.println("adding 987: " +
                 queue.offer(987, 10, TimeUnit.SECONDS));
           System.out.println("adding 578: " +
                 queue.offer(578, 10, TimeUnit.SECONDS));
           System.out.println("adding 852: " +
                 queue.offer(852, 10, TimeUnit.SECONDS));
   
           // Check whether queue is full or not
           if (queue.remainingCapacity() == 0) {
               System.out.println("queue is full");
               System.out.println("queue contains " + queue);
           }
           else {
               System.out.println("queue is not full");
               System.out.println("queue contains " + queue);
           }
   
           // Try to add more elements
           System.out.println("adding 546: " +
                     queue.offer(546, 10, TimeUnit.SECONDS));
       }
   }
   Output:

   adding 423: true
   adding 456: true
   adding 987: true
   adding 578: true
   adding 852: true
   queue is full
   queue contains [433, 456, 987, 578, 852]
   adding 546: false
   

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