JParabola

import java.awt.Graphics;

public class JParabola extends JOxy {

    private double a, b, c;

    public JParabola() {
        setA(1.0);
        setB(0.0);
        setC(0.0);
    }

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        int w = getWidth() - 1;
        double x0 = 0.0, y0 = 0.0;
        for (int i = 0; i < w; i++) {
            double x = xr(i);
            double y = getA() * x * x + getB() * x + getC();
            if (i == 0) {
                x0 = x;
                y0 = y;
            } else {
                g.drawLine(xg(x0), yg(y0), xg(x), yg(y));
                x0 = x;
                y0 = y;
            }
        }
    }

    public double getA() {
        return a;
    }

    public final void setA(double a) {
        this.a = a;
        repaint();
    }

    public double getB() {
        return b;
    }

    public final void setB(double b) {
        this.b = b;
        repaint();
    }

    public double getC() {
        return c;
    }

    public final void setC(double c) {
        this.c = c;
        repaint();
    }

}