Can you invoke a method on an object in creation of a constructor?

Question

I created a subclass named Ball of GOval. I would like to create a black ball. In order for this to work I tried this:

Within a class I create a new Ball object.

Ball ball = new Ball(0,0,200);

This invokes this constructor in Ball (which extends GOval)

public Ball(double xPos, double yPos, double diameter){
    super(xPos, yPos, diameter, diameter);
}

I would like also initialise the color as well as set the color filled within this constructor. The problem is that these are methods you invoke on an object. For instance this works:

Ball ball = new Ball(0,0,200);
ball.setFillColor(Color.BLACK)
add(playball);

But what I really want is do these last two instructions in the construction in the ball class like this:

public Ball(double xPos, double yPos, double diameter){
        super(xPos, yPos, diameter, diameter);
        setFillColor(Color.BLACK);
    }

Thank you for your replies: I got it working with:

setFilled(true);
setColor(Color.BLACK);

This probably works because I call the constructor of GOval with super, and then I call these methods (setFilled and setColor) on that object?

Of course you can; it's just a method. Be wary of calling subclass methods, though. In any case, simply trying it would have almost certainly been faster. — Dave Newton
– Dave Newton, Commented Nov 11, 2014 at 16:06
This is the exact intent of constructors (and initialisation blocks) — raphaëλ
– raphaëλ, Commented Nov 11, 2014 at 16:10

usha · Accepted Answer · 2014-11-11 16:06:26Z

1

Since fillColor is an attribute on Ball class, why can't you set it directly instead of calling the method

public Ball(double xPos, double yPos, double diameter){
    super(xPos, yPos, diameter, diameter);
    this.fillColor = Color.BLACK;
}

answered Nov 11, 2014 at 16:06

usha

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2 Comments

Dave Newton Over a year ago

Because that's not necessarily the only thing that setFillColor does. Not saying this is the case, but it may circumvent proper encapsulation.

Joop Over a year ago

fillColor is declared private within the constructor of GOval so that's not possible. And if I try to declare an instance variable myself within Ball with Color fillColor I get no errors but it also doesn't change the color. Too bad. However I got it working now!

Mahesh Acharya · Accepted Answer · 2014-11-11 16:08:21Z

1

Yes you can call other methods inside the constructor.

answered Nov 11, 2014 at 16:08

Mahesh Acharya

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