无法将对象添加到优先级队列

Question

I need to add a Jedi object to a queue. None of the add methods that I know are working and all give the "cannot find symbol - method add(jedi1).I didn't learn much about Queues in my last class so I'm not exactly sure what I'm doing. Other things to note are 3 specifics of this.

1)Modify the heap operations to keep the maximum – rather than the minimum – element in the root. Refer to the Heap lab assignment for the algorithm.

2) Utilize an array with a varying size limit (if <10% utilization reduce it by half; if full, double the size).

3) Implement the heap to receive any generic object with a comparable method.

4) Allow for duplicate value with the following rule: If a duplicate value is entered, the new element with similar value should be considered to have less priority than an existing element.

    public class PriorityQueue<JediQ>
    {
        Scanner reader = new Scanner(System.in);
        public void main(String[] args)
    {
       while (true)
    {
        System.out.println("Please select an option");
        System.out.println("1 - Add a Jedi ");
        System.out.println("2 - Remove an element");
        System.out.println("3 - Print head value");
        System.out.println("4 - Compare value to head value");
        System.out.println("5 - Print Array");
        System.out.println("6 - Exit");
        int x = 0;
        x = reader.nextInt();

        if (x == 1)
        {
            PriorityQueue<JediQ> line = new PriorityQueue<JediQ>();
            System.out.println("Enter the name of the Jedi");
            String Name = reader.next();
            System.out.println("Enter the midi count");
            double midi = reader.nextInt();

            Jedi jedi1 = new Jedi(Name, midi);

            line.add(jedi1);

            System.out.print("Jedi was added");
        }
        if (x == 6)
        {
            System.exit(0);
        }
    }
}

}

Answer 1

Your problem is a vast lack of basic knowledge about everything; so I give you some things to start with:

First of all, that error message means: your implementation of that PriorityQueue ... does not have an add() method. Because: you didn't write it! So you start with something like:

public class PriorityQueue<T> {
  public void add(T newElement) { ...

Which leads to the second major problem: the usage of generic types. As you can see in my example, you say: "my queue class, should be accepting any kind of object". And only later on, when instantiating a queue object; then you declare that this instance should be for Jedis, like:

PriorityQueue<Jedi> jedis = new PriorityQueue<>();
jedies.add(lukeSkywalkerHisUnknownCousin);

But of course, the real fun within this exercise is the implementation of a priority queue, so that it provides all the methods that a queue should have; and that they work as outlined in your assignment! And obviously, that is your assignment, so I leave that as exercise to the reader!

Final hint: if you want to understand the methods you ought to implement, you can have a look at java's own PriorityQueue and its methods!

Answer 2

Use below method.

   line.offer(yourObject);

Please read the basics of collections framework. You able to add/ modify / delete objects out of any collections because the wrapper classes have provided the methods for that. For eg. When you add int ( that becomes Integer as collection only stores Object). the default Comparator is used. as below:

    public class PriorityQueueExample
    {
        public static void main(String[] args)
        {
            //Creating a PriorityQueue with default Comparator.

            PriorityQueue<Integer> pQueue = new PriorityQueue<Integer>();

            //Inserting elements into pQueue.

            pQueue.offer(21);

            pQueue.offer(17);

            //Removing the head elements

            System.out.println(pQueue.poll()); 

To add custom objects in any collection you need to use either Comparator or Comparable.

   class JediQ
        {
            String name;

            int midi;

            //Constructor Of JediQ

            public JediQ(String name, int midi)
            {
                this.name = name;

                this.midi = midi;
            }

            @Override
            public String toString()
            {
                return name+" : "+midi;
            }
        }

   and then adding the object as below:

            class MyComparator implements Comparator<JediQ>
        {
            @Override
            public int compare(JediQ e1, JediQ e2)
            {
                return e1.name - e2.name;
            }
        }


        MyComparator comparator = new MyComparator();

        PriorityQueue<JediQ> pQueue = new PriorityQueue<JediQ>(7, comparator);
        pQueue.offer(new JediQ("AAA", 150));