How do I make my GObject outline thicker?

Question

I am trying to create a small circle and a big circle

GOval Bubbles = new GOval(0, 0, 500, 500);
    Bubbles.setColor (Color.blue);
    Bubbles.setFilled (true);
    Bubbles.setFillColor (Color.blue);
    double x = Bubbles.getWidth()/2;
    double v = Bubbles.getHeight()/2;

    add (Bubbles);


    GOval Bubbletea = new GOval (100,100);
    Bubbletea.setColor (Color.cyan);
    add (Bubbletea,x-Bubbletea.getWidth()/2,v-Bubbletea.getWidth()/2);

But the result is a blue, filled large circle, and a skinny, thin small circle. How do I make the this small circle more thick?

And are there also ways that make other GObjects thicker? Thanks!