Question

Create a Java application that allows user to build a Priority Queue of Circle Elements (i.e., priority based on the radius of the circle). The application must be menu controlled similar to Project 4 and provide the following. Allow insertion of a "Circle" object/structure in the Priority Queue data structures. Allow display of all elements from Priority Queue data structure by Invoking a method/function "DisplayPriorityQueue" (uses "DeQueue" method). Allow for deletion of the Queue

This is what I have so far. I am running into issues using  PriorityQueue<>

Circle Class that calculates. I want the PQ to use the final calculation to prioritize the lowest radius entered.

class Circle
{
    private double radius;
    Circle()
    {
        radius = 0; // initialize to 0
    }


    void setRadius(double radius) {
        this.radius = radius;
    }

    private double calculateArea()
    {
        return Math.PI * (radius * radius); // calculation to determine area of the circle
    }

    public String toString()
    {
        return String.format("Radius : %.2f , Area %.2f\n", radius, calculateArea()); // formatted to two decimal
    }
}

Main Class

import java.util.*;

class Main
{
    //create a scanner class
    private static final Scanner console=new Scanner(System.in);
    private static Stack<Circle>circleStack = null;
    private static Queue<Circle>circleQueue = null;
    public static void main(String[] args)
    {
        //create Stack of Circle
        circleStack = new Stack<>();
        //create a Queue of Circle
        circleQueue = new LinkedList<>();
        int selection;
        //call ui method
        selection = ui();
        while(selection != -1)
        {
            switch(selection)
            {
                case 1:
                    createCircleStack();break;
                case 2:
                    createCircleQueue();break;
                case 3:
                    displayStackElement();break;
                case 4:
                    displayQueueElement();break;
                case 5:
                    deleteStackElement();break;
                case 6:
                    deleteQueueElement();break;
            }
            selection = ui();
        }
        System.out.println("Quitting");
    }

    //Method to remove circle object from stack
    private static void deleteStackElement()
    {
        System.out.println("Deleting element from stack");
        System.out.println(circleStack.pop());
    }
    //Method to remove circle object from Queue
    private static void deleteQueueElement()
    {
        System.out.println("Deleting element from Queue");
        System.out.println(circleQueue.remove());
    }
    //Method to display stack element
    private static void displayStackElement()
    {
        System.out.println("Element in stack :" + circleStack.peek());
    }
    //Method to display queue element
    private static void displayQueueElement()
    {
        System.out.println("Element in queue :" + circleQueue.peek());
    }
    //Method to create stack element
    private static void createCircleStack()
    {
        double radius;

        System.out.println("Enter radius of any circle :");
        radius = Double.parseDouble(console.nextLine());

        Circle circle = new Circle();

        circle.setRadius(radius);
        circleStack.push(circle);
    }
    //Method to create circle on queue
    private static void createCircleQueue()
    {
        double radius;

        System.out.println("Enter radius of Circle :");
        radius = Double.parseDouble(console.nextLine()); //parse int

        Circle circle = new Circle();

        circle.setRadius(radius);

        //Adds circle object to queue
        circleQueue.add(circle);

    }




    //UI method that prompts user for the various required selections
    private static int ui()
    {
        System.out.println("1. Add circle to stack");
        System.out.println("2. Add a circle to queue");
        System.out.println("3. Display stack");
        System.out.println("4. Display queue");
        System.out.println("5. Pop circle fom the stack");
        System.out.println("6. Deque circle");

        System.out.println("Enter your selection[1-6] or enter -1 to exit: "); // exit program

        /*
        parseInt to convert strings to int
         */

        return Integer.parseInt(console.nextLine());
    }
}

Answer 1

import java.util.Comparator;
import java.util.PriorityQueue;
import java.util.Scanner;

class Circle {
        private double radius;

        Circle() {
                radius = 0; // initialize to 0
        }

        public Circle(double radius) {
                this.radius = radius;
        }

        public double getRadius() {
                return radius;
        }

        void setRadius(double radius) {
                this.radius = radius;
        }

        private double calculateArea() {
                return Math.PI * (radius * radius); // calculation to determine area of the circle
        }

        public String toString() {
                return String.format("Radius : %.2f , Area %.2f\n", radius, calculateArea()); // formatted to two decimal
        }
}

public class CirclePQ {

        // create a scanner class
        private static final Scanner console = new Scanner(System.in);
        private static PriorityQueue<Circle> circleQueue = null;

        // UI method that prompts user for the various required selections
        private static int ui() {
                System.out.println("1. Add circle to queue");
                System.out.println("2. Display queue");
                System.out.println("3. Deque circle");

                System.out.println("Enter your selection[1-3] or enter -1 to exit: "); // exit program

                return Integer.parseInt(console.nextLine());
        }

        // Method to create circle on queue
        private static void createCircleQueue() {
                System.out.println("Enter radius of Circle :");
                double radius = Double.parseDouble(console.nextLine()); // parse int

                Circle circle = new Circle(radius);

                // Adds circle object to queue
                circleQueue.add(circle);
        }

        // Method to display queue element
        private static void displayQueueElement() {
                for(Object o: circleQueue.toArray()) {
                        System.out.println(o);
                }
        }

        // Method to remove circle object from Queue
        private static void deleteQueueElement() {
                System.out.println("Deleting element from Queue");
                System.out.println(circleQueue.remove());
        }

        public static void main(String[] args) {
                
                // Note that, a priority queue is an ordered collection, hence we need to pass
                // a comparator, so that we can organize the elements inside the queue
                circleQueue = new PriorityQueue<>(new Comparator<Circle>() {

                        @Override
                        public int compare(Circle o1, Circle o2) {
                                if (o1.getRadius() > o2.getRadius()) {
                                        return 1;
                                }
                                if (o1.getRadius() < o2.getRadius()) {
                                        return -1;
                                }
                                return 0;
                        }
                });

                int selection;
                // call ui method
                selection = ui();
                while (selection != -1) {
                        switch (selection) {
                        case 1:
                                createCircleQueue();
                                break;
                        case 2:
                                displayQueueElement();
                                break;
                        case 3:
                                deleteQueueElement();
                                break;
                        }
                        System.out.println();
                        selection = ui();
                        System.out.println();
                }
                System.out.println("Quitting");
        }

}

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