import java.awt.AlphaComposite;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.geom.Ellipse2D;
import java.awt.geom.Rectangle2D;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

class Surface extends JPanel {

    private Rectangle2D rect;
    private Ellipse2D ellipse;
    private float alpha_rectangle;
    private float alpha_ellipse;

    public Surface() {
        
        initSurface();
    }
    
    private void initSurface() {
        
        this.addMouseListener(new HitTestAdapter());

        rect = new Rectangle2D.Float(20f, 20f, 80f, 50f);
        ellipse = new Ellipse2D.Float(120f, 30f, 60f, 60f);

        alpha_rectangle = 1f;
        alpha_ellipse = 1f;        
    }

    private void doDrawing(Graphics g) {

        Graphics2D g2d = (Graphics2D) g;

        g2d.setColor(new Color(50, 50, 50));

        RenderingHints rh = new RenderingHints(RenderingHints.KEY_ANTIALIASING,
                RenderingHints.VALUE_ANTIALIAS_ON);

        rh.put(RenderingHints.KEY_RENDERING,
                RenderingHints.VALUE_RENDER_QUALITY);

        g2d.setRenderingHints(rh);

        g2d.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER,
                alpha_rectangle));
        g2d.fill(rect);

        g2d.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER,
                alpha_ellipse));
        g2d.fill(ellipse);
    }

    @Override
    public void paintComponent(Graphics g) {

        super.paintComponent(g);
        doDrawing(g);
    }

    class RectRunnable implements Runnable {

        private Thread runner;

        public RectRunnable() {
            
            initThread();
        }
        
        private void initThread() {
            
            runner = new Thread(this);
            runner.start();
        }

        @Override
        public void run() {

            while (alpha_rectangle >= 0) {
                
                repaint();
                alpha_rectangle += -0.01f;

                if (alpha_rectangle < 0) {
                    alpha_rectangle = 0;
                }

                try {
                    
                    Thread.sleep(50);
                } catch (InterruptedException ex) {
                    
                     Logger.getLogger(Surface.class.getName()).log(Level.SEVERE, 
                             null, ex);
                }
            }
        }
    }

    class HitTestAdapter extends MouseAdapter
            implements Runnable {

        private RectRunnable rectAnimator;
        private Thread ellipseAnimator;

        @Override
        public void mousePressed(MouseEvent e) {
            
            int x = e.getX();
            int y = e.getY();

            if (rect.contains(x, y)) {

                rectAnimator = new RectRunnable();
            }

            if (ellipse.contains(x, y)) {

                ellipseAnimator = new Thread(this);
                ellipseAnimator.start();
            }
        }

        @Override
        public void run() {

            while (alpha_ellipse >= 0) {

                repaint();
                alpha_ellipse += -0.01f;

                if (alpha_ellipse < 0) {

                    alpha_ellipse = 0;
                }

                try {
                    
                    Thread.sleep(50);
                } catch (InterruptedException ex) {
                    
                    Logger.getLogger(Surface.class.getName()).log(Level.SEVERE, 
                        null, ex);
                }
            }
        }
    }
}

public class HitTesting extends JFrame {

    public HitTesting() {
        
        setTitle("Hit testing");
        
        add(new Surface());
        
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(250, 150);
        setLocationRelativeTo(null);           
    }

    public static void main(String[] args) {
        
        SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {

                HitTesting ht = new HitTesting();
                ht.setVisible(true);
            }
        });     
    }
}