The time complexity of "contains" is O (n)ġ. The Time complexity of "peek" operation is O (1). Remove (Object o): removing a specific element from the Priority Queue has a time complexity of O (n).īut remember creating Priority Queue from the existing array the time complexity is O (n) Time complexity of enqueuing/dequeuing elements from the Priority Queue is O (log n). In case if the queue is empty, "remove" throws "NoSuchElementException". remove: The "remove" method returns and removes the head element of the Priority Queue. contains: The "contains" method checks whether the element exists in the queue, if the element exists it returns true. peek: The "peek" method returns the head element of the queue without deleting it. In case if the queue is empty, "poll" returns null. 
poll: The "poll" method returns and removes the head element of the Priority Queue.On the other hand, offer returns false in case no space is available. It inserts the element to the Priority Queue.īoth methods perform the same operation with only 1 difference between the two, the add throws "IllegalStateException" if no space is available in the size restricted queue else it returns true. offer: The "offer" method also does the same.add: The "add" method inserts an element to the Priority Queue.The article covers 6 important methods from the Priority Queue object. Max Priority Queue is the reverse of Min, in Max Priority Queue the elements are in descending order and the greatest element is at the head of the queue. The Priority Queue can be called as Min Heap or Min Priority Queue when the ordering of elements is in ascending order and the smallest element is at the head of the queue. Priority Queue allows duplicate values.Priority Queue only works for "Comparable" Objects.
Priority Queues are not thread-safe, the thread-safe version is PriorityBlockingQueue. Priority Queues does not allow "null" values. Priority Queues are not bounded by the capacity meaning we cannot provide the size of the queue then it’s ideal to say these are unbounded queues. In Priority Queue sort order is not stable if two elements that are in the same position as per the comparator will not necessarily be removed in the same order as they were inserted. If no Custom Comparator is attached, then the elements are stored in Natural Order. Priority Queue or Heap is an important Data structure that is a queue, but it doesn’t store the elements in FIFO order, but it stores the elements based on Custom Comparator which is attached during Priority Queue creation. In a nutshell, the article is a practical primer on Heap Data structure. 
The article also explains the Time Complexity of every operation and at the end, it covers some important problems that can be solved using Priority Queue.
Min heap and max heap using priority queue java how to#
This article covers how to work with Comparator in Priority Queue. The article explains what Heap (Priority Queue) in Java is, its characteristics, understanding Min Heap / Max Heap, and explains a few important Java Priority Queue API methods.
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