java - 更改 Java 计时器中的延迟

Question

我正在尝试编辑我的计时器，以便每调用 25 次 repaint() ，计时器触发速度就会减半。所以前25次是500；然后接下来的 25 乘以 250；等等。

两个“对于有经验的人来说很容易”问题:

1) 为什么 Eclipse 让我将变量设为静态(或者不编译)？

2)程序似乎没有达到我将速度减半并将延迟设置为新速度的功能。这是为什么？我该如何修复它？

public class MovingCircle extends JFrame implements ActionListener {

    Ellipse2D.Double myEllipse;
    Rectangle2D.Double backgroundRectangle;
    private static int paintCount = 0;
    private static int speed = 500;

    public MovingCircle() {

        //Make the ellipse at the starting position
        myEllipse = new Ellipse2D.Double( 30, 30, 20, 20 );

        //Make the background rectangle to "erase" the screen
        backgroundRectangle = new Rectangle2D.Double( 0, 0, 400, 300 );
    }

    public static void main(String[] args ) {

        MovingCircle b = new MovingCircle();
        b.setSize( 400, 300 );
        b.setVisible(true);
        b.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );

        Timer t = new Timer(500, b );
        t.start();

        if(paintCount % 25 == 0) {

            t.setDelay((int)(speed / 2));
            speed = (int)(speed / 2);
            System.out.println(speed);
        }
  }

    public void actionPerformed( ActionEvent ae ) {

        //This will be called by the Timer
        myEllipse.setFrame( myEllipse.getX()+1, myEllipse.getY()+1, myEllipse.getWidth(), myEllipse.getHeight());  
        //Move 1 x-pixel and 1 y-pixel every 50 milliseconds ^
        repaint();
    }

    public void paint(Graphics g) {

        paintCount++;     // Incremenets by one for every repaint().
        System.out.println(paintCount);
        int isPaintTen = (int)(paintCount / 10);  // Divid current count by 10.
        Graphics2D g2 = (Graphics2D)g;

        if((isPaintTen % 2) == 0){      // Take modulus to set if #/10 is odd or even.

            g2.setColor( Color.YELLOW );
            g2.fill( backgroundRectangle );
            g2.setColor( Color.RED );
            g2.draw( myEllipse );
        }

        else if((isPaintTen % 2) == 1) {

            g2.setColor( Color.RED );
            g2.fill( backgroundRectangle );
            g2.setColor( Color.YELLOW);
            g2.draw( myEllipse );  
        }
   }

}

Answer 1

1. 在您的示例中，paintCount 和 speed 必须是静态的，因为您在没有实例的情况下从方法 main( )，它本身是静态的。为了避免将它们设为静态，您可以将它们引用为 b.paintCount 和 b.speed。

2. 修改计时器的代码需要移至 paint() 方法中。这意味着您的 Timer 实例需要成为实例变量，并且您可能应该在构造函数中创建并启动计时器。顺便说一句，这些更改还要求将 paintCount 和 speed 设为“非静态”。

你最终应该得到这样的结果:

public class MovingCircle extends JFrame implements ActionListener{
    Ellipse2D.Double myEllipse;
    Rectangle2D.Double backgroundRectangle;
    private int paintCount = 0;
    private int speed = 500;
    private Timer tmr;

    public MovingCircle() {
        //Make the ellipse at the starting position
        myEllipse = new Ellipse2D.Double( 30, 30, 20, 20 );

        //Make the background rectangle to "erase" the screen
        backgroundRectangle = new Rectangle2D.Double( 0, 0, 400, 300 );

        this.tmr = new Timer(500, this);
        tmr.start();
    }

    public static void main(String[] args ) {
        MovingCircle b = new MovingCircle();
        b.setSize( 400, 300 );
        b.setVisible(true);
        b.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
    }

    public void actionPerformed( ActionEvent ae ) {
        //This will be called by the Timer
        myEllipse.setFrame( myEllipse.getX()+1, myEllipse.getY()+1, myEllipse.getWidth(), myEllipse.getHeight());   //Move 1 x-pixel and 1 y-pixel every 50 milliseconds
        repaint();
    }

    public void paint(Graphics g) {
        paintCount++;     // Incremenets by one for every repaint().
        System.out.println(paintCount);

        if(paintCount % 25 == 0){
            tmr.setDelay((int)(speed / 2));
            speed = (int)(speed / 2);
            System.out.println(speed);
        }

        int isPaintTen = (int)(paintCount / 10);  // Divid current count by 10.
        Graphics2D g2 = (Graphics2D)g;
        if((isPaintTen % 2) == 0){       // Take modulus to set if #/10 is odd or even.
            g2.setColor( Color.YELLOW );
            g2.fill( backgroundRectangle );
            g2.setColor( Color.RED );
            g2.draw( myEllipse );

        } else if((isPaintTen % 2) == 1) {
            g2.setColor( Color.RED );
            g2.fill( backgroundRectangle );
            g2.setColor( Color.YELLOW);
            g2.draw( myEllipse );    
        }
    }
}