Casting Object to another type

[green_river48]

I have a problem with type casting!

public class MyCollection<E>{

   protected E[] elements;
   protected int top;
   public static final int SIZE = 10;
   
   public MyCollection() {
        [B]elements = (E[]) new Object[SIZE];[/B]
        top = -1;
    }
}
...
public class Test {
   
       public void draw(MyCollection<? extends Shape> list){
        for( int i = 0 ; i<=list.top ; i++)
           [B] list.elements[i].[/B]draw(); // compile error - can't cast Object to Shape
        
       }

    public static void main(String[] args) {
        MyCollection<Shape> list = new MyCollection<Shape>();
        Test test = new Test();

        list.push(new Circle());         // extends Shape , push a new Circle to list
        list.push(new Square());       // extends Shape
        list.push(new Triangle());      // extends Shape

        test.draw(list);
    }
}

how should i do ?

[Eranga]

Before that,

list.elements[i].draw();

where you implement this draw() method? In other words, did you implement an interface or what you've done on list?

[green_river48]

Before that,

list.elements[i].draw();

where you implement this draw() method? In other words, did you implement an interface or what you've done on list?

yeah , this is an abstract method of class Shape and overrided in classes Circle , Square and Triangle

[Eranga]

I'm confusing. As far as I know there is no such draw() method in the Shape interface.

[green_river48]

I'm confusing. As far as I know there is no such draw() method in the Shape interface.

if i wrote all the code , it would be very long . So i wrote the most important section :D . Sorry if it made u confused

[gcalvin]

        [B]elements = (E[]) new Object[SIZE];[/B]

This is a guess, so sorry if it turns out to be stupid...

What about...

        elements = (E[]) new Shape[SIZE];

?

-Gary-

[green_river48]

This is a guess, so sorry if it turns out to be stupid...

What about...

        elements = (E[]) new Shape[SIZE];

i've just edited :p

[himanshu19]

i am newbie an have a confusion seeing your code
Can we have more than one public class in a java program?

[DarrylBurke]

You can have at most one top-level public class in a compilation unit.
Packages

db

[himanshu19]

You can have at most one top-level public class in a compilation unit.
Packages

db

Thanks but how green_river is having two public classes in the same program
are they in different progs. file.

[JosAH]

Thanks but how green_river is having two public classes in the same program
are they in different progs. file.

Note the ellipses '...' between the two public classes; at least to me that's an indication that both class sources are stored in separate files.

kind regards,

Jos

[himanshu19]

Note the ellipses '...' between the two public classes; at least to me that's an indication that both class sources are stored in separate files.

kind regards,

Jos

thank you very much sir for the info:)

warm regards.

[green_river48]

i think downcasting only works in reference , it's no use if i try to cast a real Object to Shape, such as : Shape s1 = (Shape) new Ọbject(); and i can't call Shape's method : s1.draw() // casting error :confused: