mouseClicked event on a shape continually being repainted on a canvas

Question

I have a circle being repainted continually to show animation. I would like to have the circle flash different colors if clicked. When I tried implementing MouseListener to get a mouseClicked event, it did not work. I believe that is due to the constant repainting. Is there another way to have this circle bounce around and still catch a mouse click? I added a KeyEvent to test, and it worked fine. There is no "main" as this was called from another program.

import java.awt.*;
import java.awt.event.KeyEvent;
import java.util.Random;
import java.util.Timer;

public class Catch extends Canvas {

    int xCor, yCor, xMove, yMove;
    Color currentColor;
    Random ranNumber;
    boolean flashing = false;

    public Catch() {
        enableEvents(java.awt.AWTEvent.KEY_EVENT_MASK);
        requestFocus();
        xCor = 500;
        yCor = 350;
        xMove = 5;
        yMove = 5;
        currentColor = Color.black;
        ranNumber = new Random();
        Timer t = new Timer(true);
        t.schedule(new java.util.TimerTask() {
            public void run() {
                animate();
                repaint();
            }
        }, 10, 10);

    }

    public void paint(Graphics g) {
        g.setColor(currentColor);
        g.fillOval(xCor, yCor, 20, 20);
    }

    public void processKeyEvent(KeyEvent e) {
        if (e.getID() == KeyEvent.KEY_PRESSED) {
            if (e.getKeyCode() == KeyEvent.VK_SPACE) {
                flashing = !flashing;
            }
        }
    }

    public void animate() {
        xCor += xMove;
        yCor += yMove;

        // and bounce if we hit a wall
        if (xCor < 0 || xCor + 20 > 1000) {
            xMove = -xMove;
        }
        if (yCor < 0 || yCor + 20 > 700) {
            yMove = -yMove;
        }

        if (flashing) {
            int r = ranNumber.nextInt(256);
            int g = ranNumber.nextInt(256);
            int b = ranNumber.nextInt(256);
            currentColor = new Color(r, g, b);
        }
    }

    public boolean isFocusable() {
        return true;
    }
}

Answer 1

Your approach is a little out of date, we don't tend to use enableEvents any more, but instead make use of a number of different "observers" which provide notification about certain events.

I'd start by having a look at Painting in AWT and Swing and Performing Custom Painting and How to Write a Mouse Listener

I'd also avoid using KeyListener and instead use the Key Bindings API which was designed to overcome many of the shortcommings of KeyListener.

While cutting edge would be to use JavaFX, if you have a knowledge of AWT, then stepping up to Swing would simpler, for example:

import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.Rectangle;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.geom.Ellipse2D;
import java.awt.geom.Rectangle2D;
import java.util.Random;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class Test {

    public static void main(String[] args) {
        new Test();
    }

    public Test() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        private Ball ball;

        public TestPane() {
            ball = new Ball();
            Timer timer = new Timer(40, new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    ball.update(getSize());
                    repaint();
                }
            });
            timer.start();

            addMouseListener(new MouseAdapter() {
                @Override
                public void mousePressed(MouseEvent e) {
                    ball.setHighlighted(ball.wasClicked(e.getPoint()));
                }
            });
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(200, 200);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();
            ball.paint(g2d);
            g2d.dispose();
        }

    }

    public class Ball {

        private int radius = 10;
        private int xDelta, yDelta;
        private Ellipse2D shape = new Ellipse2D.Double(0, 0, radius * 2, radius * 2);
        private boolean highlighted;
        private int cycleCount;

        public Ball() {
            Random rnd = new Random();
            xDelta = rnd.nextInt(3) + 1;
            yDelta = rnd.nextInt(3) + 1;
        }

        public void update(Dimension bounds) {
            Rectangle shapeBounds = shape.getBounds();
            shapeBounds.x += xDelta;
            shapeBounds.y += yDelta;
            if (shapeBounds.x + shapeBounds.width > bounds.width) {
                shapeBounds.x = bounds.width - shapeBounds.width;
                xDelta *= -1;
            } else if (shapeBounds.x < 0) {
                shapeBounds.x = 0;
                xDelta *= -1;
            }
            if (shapeBounds.y + shapeBounds.height > bounds.height) {
                shapeBounds.y = bounds.height - shapeBounds.height;
                yDelta *= -1;
            } else if (shapeBounds.y < 0) {
                shapeBounds.y = 0;
                yDelta *= -1;
            }
            shape.setFrame(shapeBounds);

            if (highlighted) {
                cycleCount++;
                if (cycleCount > 12) {
                    highlighted = false;
                }
            }
        }

        public boolean wasClicked(Point p) {
            return shape.contains(p);
        }

        public void setHighlighted(boolean value) {
            highlighted = value;
            cycleCount = 0;
        }

        public void paint(Graphics2D g) {
            if (highlighted) {
                g.setColor(Color.RED);
            } else {
                g.setColor(Color.BLUE);
            }
            g.fill(shape);
        }
    }

}

You should also have a look at How to use Swing Timers