Java Priority Queue: What are they?

The PriorityQueue in Java is opted when objects in the frontline are meant to be executed based upon priority. Not just that, it is also known that the queue follows the algorithm known as First-In-First-Out. However, there are times when these elements in the queue are required to be processed in accordance with priority. This is when priority queue comes into consideration.


PriorityQueue in Java serves as the section of java.util package, which is also the generic implementation for priority-based Java queue. In simple terms, a queue can be defined as the data structure which determined the specific norms for insertion process & items retrieval from the store. This idea is particularly similar to the total count of people standing amid the queue.

The person standing first in this queue is eligible for the first chance to obtain anything while the last in line gets chance towards the end. People can be added towards the queue’s end or its tail end. Adding any item to a pre-defined queue is termed as Enqueue process. Any item removed in this queue is most the one at the front of the line. This is termed as dequeue. The central idea is order of elements in the FIFO pattern (first-in-first-out).

This can be termed as the purest form of architecture with jointly designated term that defines what queue elaborates. It also helps understand how it can be simulated on the computer. A store in the Java PriorityQueue is mostly represented in the form of simple array with storage as well as retrieval processes containing their defined norms. Some unique form of standards is imposed for the priority queue above this.

Key Points of Java PriorityQueue

  • A comparator needs to be provided for the constructor when the PriorityQueue is instantiating. After this, the items’ order in PriorityQueue is decided by being based upon a Comparator supplied in this case.
  • If there is no provisioning of the Comparator, then the base order for this Collection shall be used to create an order in the elements.
  • This Collection doesn’t allow null sets.
  • The Queue Head is termed as the least essential item in this order.
  • Ordering properties amid the elements for PriorityQueue are decided based upon the arbitrary.
  • The PriorityQueue isn’t synchronized. The PriorityBlockingQueue serves as the thread-safe PriorityQueue counterpart.
  • PriorityQueue has been unbounded as it grows in a dynamic manner based upon the total elements in this Queue. It has the internal capacity to grow dynamically at any defined time. Further, it is known to increase as features are included in the same. Policy for internal size & increment cannot be specified/ standardized.
  • The iterator () for this PriorityQueue doesn’t guarantee the traversal of Queue elements into the given order.
  • In terms of performance, the methods remove () & contains () take the linear time. These elements include an element (), peek (), and size () which takes a fixed time. On the other hand, features such as offer (), remove (), and poll () tend to take O (log n) time as compared to the prior elements.
  • Add () and offer () serve as the methods for Queue interface which is implemented with the help of Priority Queue. They also behave in the same manner as seen in the PriorityQueue & there is no other difference amid them.

PriorityQueue Java Constructors

The PriorityQueue classes tend to cater 6 different methodologies for construction of priority queue in Java software development services.

  • PriorityQueue (): It is the constructs null queue with the default form of initial capacity (11) which orders its base elements in accordance with the natural ordering.
  • PriorityQueue (Collection c): This constructs form is a null queue that contains elements in specified collections.
  • PriorityQueue (int initialCapacity): This constructs form is an empty queue that comes with a specified type of initial capacity that orders the elements in accordance with the natural ordering.
  • PriorityQueue (int initialCapacity, Comparator comparator): This constructs form is an empty queue that comes with a specified type of initial capacity that orders its base elements in accordance with specified comparator.
  • PriorityQueue (PriorityQueue c): This constructs form of the null queue contains elements in specified section of priority queue.
  • PriorityQueue (SortedSet c): It houses an empty queue that contains elements specified within a sorted form of set.

PriorityQueue Java Methods

The class for PriorityQueue methods listed below plays a vital role in the Java methods:

  • Boolean add (object): This method inserts a specified element that enters the priority queue.
  • Boolean offer (object): This method inserts a specified element that is embedded into the priority queue.
  • Boolean remove (object): It helps remove the single instances of the specified element from queue, when present.
  • Object poll (): This method retrieves as well as removes the queue’s head or returns it as a null set if the queue is empty.
  • Object element (): It retrieves but doesn’t remove the same. It is the head for the queue, which can return null when the queue is determined as empty.
  • Object peek (): It retrieves but doesn’t actually remove the queue head. If the queue is particularly empty, the object peek returns null.
  • Void clear (): It tends to remove all elements from the priority queue.
  • Comparator comparator (): It returns comparator used for ordering the elements of this queue. It is also deemed null when the queue is actually sorted in accordance with the natural order of the elements.
  • Boolean contains (Object o): It returns true when the queue contains a specified element.
  • Iterator iterator (): It returns the iterator atop the elements present in the queue.
  • Int size (): It returns the total number of the elements that are a part of the queue.
  • Object[] to Array(): It tends to return the array containing elements of concern in the queue.


Apart from the priority queue norms that are known in general, it should be ensured that the item picked off from this list needs to be of highest priority. The method by which Java tends to impose its priority rule in comparison with the usual queue form is by concocting the principal elements of the ordering. This particular order can then be customized in accordance with the requirements of a programmer, or the given set remains default. This is the general essence of implementation of the priority queue in the Java variant.