重新绘制方法无法及时工作

Question

I'm making a game in Java, and the repaint() method is misbehaving in a very odd way. Basically, I need to repaint the board before getting the AI's move. Here is my method where I'm calling it:

public void mouseClicked(MouseEvent e) {
    mouseX = e.getX();
    mouseY = e.getY();

    int button = e.getButton();
    if (button == MouseEvent.BUTTON1 || button == MouseEvent.BUTTON3) {
        int mouseR = (mouseY / SIZE);
        int mouseC = (mouseX / SIZE);

        if (mouseR >= 0 && mouseC >= 0 &&
                mouseR < board.length && mouseC < board[0].length) {
            if (board[mouseR][mouseC] == 3) {
                makeMove(mouseR, mouseC, playerColor);
                getValidMoves((playerColor % 2) + 1);
                repaint();
                getAIMove();
            }
        }

    }
    repaint();
}

getAIMove() is designed so it waits for a couple of seconds before making the move, so the player can see the results of their move before they see those of the AI. Unfortunately, although I call repaint() before getAIMove() , what happens is more like this: the player clicks where they want to move. Nothing appears to happen for a few seconds, then the results of the player's move AND the AI's move are displayed on the screen. What's going on?

Answer 1

All the code in your mouseClicked() event handler will run on the special AWT/Swing Thread.

repaint() does not repaint the GUI immediately - it schedules a repaint , (see this article ) which will also run on the Swing thread - but not until your event handler has finished - the Swing thread can only do one thing at a time!

So you won't see the results of getAIMove() until afterwards.

You probably need to run the getAIMove() logic in a separate background thread, then update the GUI (which must be done in the Swing thread, using SwingUtilities.invokeLater() or the SwingWorker helper class.)

Or, you could schedule the AI to run on the Swing thread, using invokeLater() - it will then run after the first repaint() . However, this method is undesirable (unless the AI is very fast), because your GUI will be unresponsive until the Swing thread becomes free again to handle repaints.

See also the Java tutorials on these topics:

• Concurrency
• Concurrency in Swing
• Worker threads and SwingWorker

Answer 2

A friend and I figured out a little trick to beat the queue described by @DNA - here's my new code:

public void mousePressed( MouseEvent e )
   {
      mouseX = e.getX();
      mouseY = e.getY();

      int button = e.getButton();
      if(button == MouseEvent.BUTTON1 || button == MouseEvent.BUTTON3)
      {
         int mouseR = (mouseY/SIZE);
         int mouseC = (mouseX/SIZE);

         if(mouseR >=0 && mouseC >= 0 && mouseR < board.length && mouseC < board[0].length)
         {
            if (board[mouseR][mouseC] == 3){
               makeMove(mouseR, mouseC, playerColor);
            }
         }

      } 
      repaint();
   }

   public void mouseReleased( MouseEvent e )
   {
      int button = e.getButton();
      if(button == MouseEvent.BUTTON1 || button == MouseEvent.BUTTON3)
      {
         int mouseR = (mouseY/SIZE);
         int mouseC = (mouseX/SIZE);

         if(mouseR >=0 && mouseC >= 0 && mouseR < board.length && mouseC < board[0].length)
         {
            if (board[mouseR][mouseC] == playerColor){
               getValidMoves((playerColor % 2) + 1);
               getAIMove();
               getValidMoves(playerColor);
            }
         }

      } 
      repaint();
   }

By doing the player's move when the mouse is pressed, and waiting to do the AI's move until the mouse is released, the program is allowed to complete the Swing thread and repaint the board. Thanks for all of your help!