带图形组件的Swing Timer

Question

I want to creat a circle in on a panel which appears and dissapears every 2 seconds. Here is that i have:

public class Board extends JPanel implements ActionListener {

    private final int DELAY = 2000;

    private Timer timer;

    /*
     * constructor
     */
    public Board() {

        setFocusable(true);
        initGame();
    }

    /*
     * initialize board
     */
    public void initGame() {

        timer = new Timer(DELAY, this);
        timer.start();

    }

    public void paint(Graphics g) {

        super.paint(g);
        g.setColor(Color.gray);
        // draw an oval starting at 20,20 with a width and height of 100 and
        // fill it
        g.drawOval(20, 20, 100, 100);
        g.fillOval(20, 20, 100, 100);

        g.dispose();
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        repaint();
    }
}

thank you guys. Now I wanna control my circle. But again something is wrong and it is not moving as I want.

here are new methods:

    private boolean left = false;
private boolean right = true;
private boolean up = false;
private boolean down = false;

private Timer timer;

public int x = 20;
public int y = 20;
public int x2 = 100;
public int y2 = 100;

...

    public void paint(Graphics g) {

    super.paint(g);
    if (drawCircle) {
        g.setColor(Color.gray);
        // draw an oval starting at 20,20 with a width and height of 100 and
        // fill it
        g.drawOval(x, y, x2, y2);
        g.fillOval(x, y, x2, y2);
    }
    // removes native non-Java recourses
    g.dispose();
}

public void move() {

    if (left) {
        x -= 5;
    }
    if (right) {
        x += 5;
    }
    if (up) {
        y -= 5;
    }
    if (down) {
        y += 5;
    }
}

@Override
public void actionPerformed(ActionEvent e) {

    move();
    repaint();
}

private class TAdapter extends KeyAdapter {

    public void keyPressed(KeyEvent e) {

        int key = e.getKeyCode();

        if ((key == KeyEvent.VK_LEFT) && (!right)) {
            left = true;
            up = false;
            down = false;
        }

        if ((key == KeyEvent.VK_RIGHT) && (!left)) {
            right = true;
            up = false;
            down = false;
        }

        if ((key == KeyEvent.VK_UP) && (!down)) {
            up = true;
            right = false;
            left = false;
        }

        if ((key == KeyEvent.VK_DOWN) && (!up)) {
            down = true;
            right = false;
            left = false;
        }
    }
}

/ * ** * / Solved , i just added

addKeyListener(new TAdapter());

to my Board constructor!

Answer 1

You just need to have your Timer modify some state. Try something like this:

private boolean drawCircle = false;

public void actionPerformed(ActionEvent e) {
    drawCircle = !drawCircle;
    repaint();
}

public void paintComponent(Graphics g) {
    //...
    if ( drawCircle ) {
       g.setColor(Color.gray);
       //...
    }
}

Answer 2

Aren't you supposed to formulate the question... as a question?

Anyway, add a boolean to your class, toggle it on each action event, and paint the oval only if it is true.

Edit/Notes: - Override paintComponent instead of paint - Don't dispose of a Graphics you haven't created. Either drop the line, or use g.create() to make a copy. See http://java.sun.com/products/jfc/tsc/articles/swing2d/ for details.