Why is my class not a BitmapFont if I am extending it

Question

So I have this class:

public class Font extends BitmapFont
{
    FreeTypeFontGenerator generator;
    FreeTypeFontGenerator.FreeTypeFontParameter parameter;
    public Font()
    {
        generator = new FreeTypeFontGenerator();
        parameter = new FreeTypeFontGenerator.FreeTypeFontParameter();
        parameter.size = 30;
        parameter.color = Color.WHITE;
        this = generator.generateFont(parameter);
        generator.dispose();
    }
}

But on this line:

this = generator.generateFont(parameter);

I get an error, it says: required Font, found BitmapFont.

Now I dont get it why the compiler doesnt see my Font class as a BitmapFont. Do you guys know the reason and also know how I still can make the font assign to the class itself?

Answer 1

Regardless of the mistake that Raeffaele describes in the comments, you are not understanding a fundamental thing of OO here.

Take this simple is-a example: a Cow is an Animal. But an Animal is not always a Cow. It can also be a Sheep, or a Dog. And as we all know, a Dog and a Cow are completely different, even though they both inherit from Animal.

Now we apply that to your situation. A Font is-a BitmapFont, but a BitmapFont is not always a Font.

Given that, The

generator.generateFont(parameter);

call returns a LibGDX BitmapFont instance, not an instance of your own Font class. So it would be a very bad idea to try and assign it to a variable that demands an instance of Font anyway.

---

Shorter version.

You should understand that this works because Font is-a BitmapFont:

BitmapFont font = new Font();

and this does not because BitmapFont is not a Font:

Font font = new BitmapFont();

Your code is attempting to create the second situation, just in a slightly different way.