如何在另一个上绘制图像？

Question

So I am working on a project for a class. And I've been struggling with this issue for a while now. The code below is a start screen, and when the enter key is pressed (when atTitle turns to false) I would like it to draw the next image. The problem with that is I can not think of a way for it to draw the next image when it turns to false. I've tried using ifs and whiles. Mainly the problem is that you obviously put another public void paintComponent in an if statement. And I can't carry the Graphics g variable to the KeyPressed method. I'm stuck.

public void paintComponent(Graphics g) {
    super.paintComponent(g);
    Graphics2D g2 = (Graphics2D)g;
    AffineTransform at = new AffineTransform();
    g2.setTransform(at);
    if (atTitle == true) {
        g.drawImage(titlescreen, 0, 0, this);
        if (start_visible == true) {
            g.drawImage(start_symbol, -70, 30, this);
            jf.addKeyListener(this);
        }
    }
}

public void keyTyped(KeyEvent e) {}
public void keyReleased(KeyEvent e) {}

public void keyPressed(KeyEvent e) {
    //int keyCode = e.getKeyCode();
    if (atTitle == true) {
        if (e.getKeyCode() == KeyEvent.VK_ENTER) {
            atTitle = false;
            System.out.println("It Works.");
        }
    }
}

Answer 1

If you are using JPanel you should:

panel.setFocusable(true);
panel.requestFocusInWindow();

Referenced here

Also you can call panel.revalidate() and/or panel.repaint() in the key press.

Maybe try to stay away from JPanel and Swing altogether (not suited for gaming, but for forms) and just use the graphics2D functionality with a Window, Frame and Canvas, as suggested in previous comment.

Answer 2

you need to call repaint and wait system calls to paint function. you should not keep graphic object and use it in a function is not child function of paint

as a simple canvas component, you can use this one

class Game extends Canvas implements Runnable {
        private Thread thread;
        public Game(){
            thread = new Thread(this);
            thread.start();
        }
        @Override
        public void paint(Graphics g) {
            // paint your game
        }
        public void stop(){
            thread = null;
        }
        @Override
        public void run() {
            while (thread == Thread.currentThread()){
                long ti = System.currentTimeMillis();
                repaint();
                long ti2 = System.currentTimeMillis();
                long waitTime = 60 - (ti2-ti);
                if (waitTime > 0){
                    try {
                        Thread.sleep(waitTime);
                    } catch (Exception e){

                    }

                }
            }
        }
    }