Evil Circle

package samples;

/*
 * File: GraphicsHierarchy.java
 * ----------------------------
 * This program is a stub for the GraphicsHierarchy problem, which
 * draws a partial diagram of the acm.graphics hierarchy.
 */
import acm.graphics.GOval;
import acm.program.*;
import acm.util.RandomGenerator;

import java.awt.*;
import java.awt.event.MouseEvent;

public class GraphicsProgramSample extends GraphicsProgram {

    private final static int CIRCLE_D = 40;
    private GOval myBall = null;
    private RandomGenerator rgen = RandomGenerator.getInstance();

    public void init() {
        addMouseListeners();
        drawBall();
    }

    // draws the main ball
    private void drawBall() {
        int ballX = getWidth() / 2 - CIRCLE_D / 2;
        int ballY = getHeight() / 2 - CIRCLE_D / 2;
        myBall = new GOval(ballX, ballY, CIRCLE_D, CIRCLE_D);
        myBall.setFilled(true);
        myBall.setColor(Color.BLACK);
        add(myBall);
    }

    // 1. Color on click
    public void mouseClicked(MouseEvent e) {
        Color ballsNewColor = rgen.nextColor();
        myBall.setColor(ballsNewColor);
    }

    // 2. change size on move
    public void mouseDragged(MouseEvent e) {
        // 2.1 change size
        int dx = (int) (e.getX() - (getWidth() / 2));
        int dy = (int) (e.getY() - (getHeight() / 2));
        int r = (int) Math.sqrt(dx * dx + dy * dy);
        myBall.setSize(2 * r, 2 * r);

        // 2.2 change location
        int ballX = getWidth() / 2 - r;
        int ballY = getHeight() / 2 - r;
        myBall.setLocation(ballX, ballY);
    }
}