PriorityBlockingQueue Class in Java

What is the Queue?

An abstract data structure like Stacks is a queue. A queue is open on both ends. Data is always pushed to one end, called enqueue, and removed from the other end, called dequeue. An ordered list of items called a queue is created when elements are added at the back of the list and removed from the front. As a result, it is also suggested that the queue operates under the First in, First Out (FIFO) principle.

PriorityBlockingQueue-What is it?

A priority-blocking queue is one of the members of the collection framework in Java. The Priority Blocking Queue seems to be an extended blocking queue which offers blocking retrieval procedures and follows the very same sorting principles as the PriorityQueue classes. Since adding items is unlimited, it occasionally encounters out of memory errors because of the depletion of resources. Null elements are not accepted in this class.

The Blocking Queue is indeed a group that also enables operations that hold off on fetching an element until the queue is no longer empty and delays the entry of an element till the queue is empty. All the additional operations of the Collection and Iterator interfaces are implemented by the Priority Blocking Queue class and its iterator.

A blocking queue cannot have any elements added to it, unlike a regular queue. Safety of the threads is one of the guaranteed advantages across all blocking queue solutions. Each of the techniques uses inner locks or some other type of access control to accomplish its goals.

The Utilization of a PriorityBlockingQueue

It extends the Abstract Queue class and implements the Serializable, Iterated, Collection, Blocking Queue, and Queue interfaces.

Declaration of PriorityBlockingQueue

 PriorityBlockingQueue< X > variable = new PriorityBlockingQueue< X > ();

Where X represents the different types of datatypes defined as wrapper classes.

PriorityBlockingQueue Builders

Priority blocking queues in Java can be implemented in many ways. Some of them are as follows:

• Priority blocking queue with initial size
• Priority blocking queue with defined collection
• Priority blocking queue of a certain size
• Priority blocking queue of a specific size and comparator
• Iterator-based priority blocking queue

1. Let’s see an example code in Java about printing elements of a priority blocking queue with an initial size

Code

// example java program for illustrating priority blocking queue method
import java.io.*:
import java.util.*;
import java.util.concurrent.PriorityBlockingQueue;
public class Bqueue {
   public static void main(String[] s) {
      PriorityBlockingQueue<String>prioritybq = new PriorityBlockingQueue<String>();
     prioritybq.add("Ram");
     prioritybq.add("Seetha");
     prioritybq.add("Bheem");
     prioritybq.add("Arjun");
     prioritybq.add("Bharath");
      System.out.print("Elements that are present in the priority blocking queue are ==>> " + prioritybq);
   }
}

Output

C:\ java>javac Bqueue.java
C:\java>java Bqueue
Elements that are present in the priority blocking queue are ==>> [ Ram, Arjun, Bheem, Seetha, Bharath]

2. Let’s see an example code in Java about printing elements of a priority blocking queue using the iterator method.

Code 

// A Java programme uses an iterator to implement a Priority Blocking Queue.
import java.io.*;
import java.util.*;
import java.util.concurrent.PriorityBlockingQueue;
 
public class Bqueue{
              public static void main(String[] s)
              {
             int c=7;
                             // define PriorityBlockingQueue by creating object for it
                             PriorityBlockingQueue<Integer>n = new PriorityBlockingQueue <Integer>(c);
                             n.add(26);
                             n.add(32);
                             n.add(48);
                             n.add(51);
                             n.add(68);
                             n.add(79);
                             n.add(137);
                             Iterator it = n.iterator();
// Invoke the iteration method.
System.out.print("The numbers collected from priority blocking queue are ==>> ");
// display by showing the elements of the iterator
// print the elements
                             while(it.hasNext()) {
                                           System.out.print(it.Next());
                             }
              }
}

Output

C:\java>javac Bqueue.java
C:\java>java Bqueue
The numbers collected from the priority blocking queue are ==>> 26
32
48
51
68
79
137

Simple Actions in the PriorityBlockingQueue

The simple and basic operations that are performed on the priority blocking queue are given as

1. Inserting elements
2. Removing elements
3. Iterating elements
4. Accessing elements

Inserting Elements

The element given as an input to the add method of a Priority Blocking Queue is inserted at the end of the queue by this method. When adding an element successfully, this function will return true. Otherwise, a false positive result is returned.

For example, x.add("JAVA");

Removing Elements

In this Priority Blocking Method, deletion of elements takes place. If the element passed as an input is available, this function deletes a single instance of it. If and only if the element was deleted, it returns true; otherwise, it returns false. To erase all the items at once, we use clear() method.

For example, x.clear();

Iterating Elements

In this iterator method of priority blocking queue the out may not be ordered and it is weak.

Accessing Elements

The element at the top of the Priority Blocking Queue is retrieved by the function peek() of the queue. It does not erase the Linked Blocking Queue’s head value; rather, it obtains it. This function returns null if there are no elements in the PriorityBlockingQueue. The ordering guidelines used by class Priority Queue also apply to PriorityBlockingQueue queues.

Conclusion

Concurrent trying to block queue data structure implementation using the Java Priority Blocking Queue class optimizes elements for processing. The word "blocking" has now been added to the name to emphasise that perhaps the thread might block while it waits for an item to become accessible in the queue.

Added items are arranged in a priority blocking queue in accordance with their significance. By default, the order of things in space determines the priority. A Comparator supplied at queue formation time can modify the default priority.