Why can't I implement my Vector methods on this instance of VectorQueue?

Question

The class VectorQueue here is a queue data structure implementing vector methods. In my test class at the bottom I can successfully compile code such as " myVector.enqueue(20); " where myVector is an instance of the VectorQueue class. It's actual type is Queue - see here

Queue<Integer> myVector = new VectorQueue<Integer>();

My question is this: Is there no way to use the vector methods on the instance "myVector" once it has been actualized as type Queue? I've tried the following:

((Vector<T>) myVector).insertAtRank(2,5);

I also tried making my main class VectorQueue implement Queue and Vector interfaces, but it didn't help. I wondered to myself also, why can't something have multiple actualized types?

package W7;

public class VectorQueue<T> implements Queue<T> {

public Vector<T> myVector = new ArrayVector<T>();

public void enqueue(T e) {
    myVector.insertAtRank(myVector.size(), e);
}

public T front() {
    return myVector.elemAtRank(0);
}

public T dequeue() {
    return myVector.removeAtRank(0);
}

public boolean isEmpty() {
    return myVector.isEmpty();
}

public int size() {
    return myVector.size();
}

public String toString(){
    return myVector.toString();
}

public static void main(String[] args) throws VectorFullException,
        RankOutOfBoundsException {

    Queue<Integer> myVector = new VectorQueue<Integer>();

    try {

        myVector.enqueue(10);
        System.out.println(myVector);

        myVector.enqueue(5);
        System.out.println(myVector);

        myVector.dequeue();
        System.out.println(myVector);

        myVector.enqueue(15);
        System.out.println(myVector);

        myVector.enqueue(3);
        System.out.println(myVector);

        myVector.dequeue();
        System.out.println(myVector);

        myVector.enqueue(7);
        System.out.println(myVector);

        myVector.dequeue();
        System.out.println(myVector);

        myVector.enqueue(20);
        System.out.println(myVector);

        ((Vector<T>) myVector).insertAtRank(2,5);

    } catch (VectorFullException RankOutOfBoundsException) {
        System.out.println("Error");
    }
    int total = 0;
    while(! myVector.isEmpty()){
        total += myVector.dequeue();
    }
    System.out.println("The total size of the contents: " + total);
    }
}

Answer 1

Instead of creating an instance for interface reference use your class' reference. VectorQueue<Integer> myVector = new VectorQueue<Integer>();