Difference Between PriorityQueue and TreeSet

The PriorityQueue and TreeSet both are the classes defined inside the Collection Framework. In this article, we will learn the differences between PriorityQueue and TreeSet. PriorityQueue is an implementation of Queue interface and the TreeSet is the implementation of the Set interface. There are some differences exists between them. So we have tried to list out the differences between PriorityQueue and TreeSet.

1. PriorityQueue: A PriorityQueue is used when the objects are supposed to be processed based on the priority. It is known that a Queue follows the First-In-First-Out algorithm, but sometimes the elements of the queue are needed to be processed according to the priority, that’s when the PriorityQueue comes into play. The PriorityQueue is based on the priority heap. The elements of the priority queue are ordered according to the natural ordering, or by a Comparator provided at queue construction time, depending on which constructor is used.  

PriorityQueue Demo:

Java

// Java program to demonstrate the
// working of PriorityQueue
import java.util.*;

class PriorityQueueDemo {

    // Main Method
    public static void main(String args[])
    {
        // Creating empty priority queue
        PriorityQueue<String> pQueue
            = new PriorityQueue<>();

        // Adding elements to the pQueue using add()
        pQueue.add("Geeks");
        pQueue.add("For");
        pQueue.add("Geeks");

        // Printing the top element of PriorityQueue
        System.out.println(pQueue.peek());

        // Printing the top element and removing it
        // from the PriorityQueue container
        System.out.println(pQueue.poll());

        // Printing the top element again
        System.out.println(pQueue.peek());
    }
}

Output

For
For
Geeks

2. TreeSet: TreeSet is one of the most important implementations of the SortedSet interface in Java that uses a Tree for storage. The ordering of the elements is maintained by a set using their natural ordering whether or not an explicit comparator is provided. This must be consistent with equals if it is to correctly implement the Set interface. It can also be ordered by a Comparator provided at set creation time, depending on which constructor is used. The TreeSet implements a NavigableSet interface by inheriting AbstractSet class.

TreeSet Demo:

Java

// Java code to demonstrate
// the working of TreeSet

import java.util.*;
class TreeSetDemo {

    public static void main(String[] args)
    {
        // Creating an empty TreeSet
        TreeSet<String> ts = new TreeSet<String>();

        // Elements are added using add() method
        ts.add("Geek");
        ts.add("For");
        ts.add("Geeks");

        System.out.println("Tree Set is " + ts);

        String check = "Geeks";

        // Check if the above string exists in
        // the treeset or not
        System.out.println("Contains " + check + " "
                           + ts.contains(check));

        // Print the first element in
        // the TreeSet
        System.out.println("First Value " + ts.first());

        // Print the last element in
        // the TreeSet
        System.out.println("Last Value " + ts.last());

        String val = "Geek";

        // Find the values just greater
        // and smaller than the above string
        System.out.println("Higher " + ts.higher(val));
        System.out.println("Lower " + ts.lower(val));
    }
}

Differences between PriorityQueue and TreeSet

PriorityQueue	TreeSet
PriorityQueue uses the Queue underlying data structure	TreeSet uses the Set underlying data structure.
PriorityQueue allows the duplicate elements	TreeSet doesn’t allow the duplicate elements
In PriorityQueue, apart from the root rest of the elements may or may not follow any order.	In TreeSet all the elements remain in the sorted order.
Using PriorityQueue, we can retrieve largest or smallest element in O(1) time.	TreeSet doesn’t provide a way to retrieve largest or smallest element in O(1) time, but since they are in sorted order it gets the first or last element in O(1) time.
PriorityQueue comes in JDK 1.5.	TreeSet comes in JDK 1.4.