Re: [Jsynthlib-devel] Fwd: Overriding calculateChecksum

[Jeff W. <jww...@ya...>]

--- Hiroo Hayashi <hir...@co...> wrote:
> I can hardly believe what you wrote. If override
> does not work, the Java
> environment is useless at all.  How did you confirm
> it? What happen if
> you put print statement in your
> calculateChecksum(Patch,int,int,int)?

Defies logic doesn't it? I know I have to keep
pinching myself. I've tested this numerous times both
stepping through with a debugger and using print
statements. Finally, I put together a really simple
example that demonstrates this (See below).

What I've found out is that it appears to be happening
because Driver.calculateChecksum(Patch, int, int, int)
is defined as a static method.

The attached example has a main class (StaticOverride)
along with two classes, Rectangle, which inherits from
Object, and Square which inherits from Rectangle. Both
Rectangle and Draw contain a static draw(int) method
that prints a message int number of times. Rectangle
has a non-static draw() method that calls the
draw(int) method. The main class, StaticOverride
creates an object of type Square and calls it's draw()
method. Because Square.draw() is commented out, it
calls Rectangle.draw() which in turn calls draw(int).
You would think that because draw(int) is overridden
in the Square class, that Square.draw(int) would be
called but nope, Rectangle.draw(int) is called
instead.

If you make the draw(int) methods non-static in both
the Rectangle and Square classes, then it works the
way you'd expect and the Square.draw(int) method is
called instead. (At least, that's what happens on my
system).

Go ahead and try it. If you get different results than
I did, then something's flakey either with my system
or my brain.

Here's my example:
----------------------------
import java.util.*;

public class StaticOverride {
    
    public static void main (String args[]) {
        Square aSquare = new Square();

        aSquare.draw();
    }
}


class Rectangle {
    int nbr = 2;
    
	void draw() {
		draw(nbr);
	}
    
    static void draw (int num) {
        for (int i = 0; i < num; i++) {
            System.out.println("Drawing a
rectangle.");
        }        
    }
}


class Square extends Rectangle {
    //	void draw() {
    //        draw(nbr);
    //    }
    
    static void draw (int num) {
        for (int i = 0; i < num; i++) {
            System.out.println("Drawing a square.");
        }
    }
}




		
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