Java interface method call via object

Question

I have the main method written as following:

/*
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 * and open the template in the editor.
 */
package excercise.pkg5;

/**
 *
 * @author Azraar
 */

    public class TestResizable {

    public static void main(String[] args) {

        Shape obj[] = new Shape[4];
        obj[0] = new Circle(10);
        obj[1] = new Rectangle(10, 20);
        obj[2] = new ResizableCircle(10);
        obj[3] = new ResizableRectangle(10, 20);

        for (int i = 0; i < obj.length; i++) {

            if (obj[i] instanceof ResizableCircle) {
                ResizableCircle r = (ResizableCircle) obj[i];
                obj[i].equals(r);

            }

            if (obj[i] instanceof ResizableRectangle) {
                ResizableRectangle r = (ResizableRectangle) obj[i];
                obj[i].equals(r);

            }

            System.out.println("");
            System.out.print("Object is - " + obj[i].name());
            System.out.print("\nObject Area is - " + obj[i].area());
            System.out.print("\nObject Perimeter is - " + obj[i].perimeter());
        }

    }
}

i am using ResizableRectangle r = (ResizableRectangle) obj[i]; , because resizable is an implement and ResizableRectangle and ResizableCircle are extending it and overriding the method resize.

if instanceof resizbleRectange or resizableCircle.. i need to run this resize() method..

obj[i].resize(0.5) and then it will loop out and print. but the problem is i am not getting resize method true intelisense also when i type it says cannot find sympbol...

below is the class hierarchy...

EDIT:

shape is the ROOT CLASS as you can see in the attached screenshot. i am thinking of a way to access resize method when object is an instace of ResizeableClass and ResizeableRectangle. but still unable.

Answer 1

You need to call resize() on a Resizeable reference.

That is, if obj[i] is a Resizeable, then you need to cast and then call it. It's not enough simply to assert that obj[i] refers to such an object since the compiler is simply treating it as a base class reference.

e.g.

if (obj[i] instanceof Resizeable) {
   ((Resizeable)obj[i]).resize(..);
}

Answer 2

You declared obj as

Shape obj[]

so obj[i] will return a Shape object which I'm guessing doesn't extend Resizeable.

Answer 3

Not all subclasses of Shape method implement Resizable interface. So you need to check if obj[i] is instance of Resizeable class and then call resize on it.

Answer 4

This worked at last...

    if (obj[i] instanceof ResizableCircle) {
        Resizable c = (ResizableCircle) obj[i];
        c.resize(5);

    }

    if (obj[i] instanceof ResizableRectangle) {
        Resizable r = (ResizableRectangle) obj[i];
        r.resize(10);

    }