在Java定時器中更改延遲

Question

我試圖編輯我的定時器，以便每25次重繪（）稱爲定時器啓動速度減半。所以前25次是500。那麼下一個25倍的250;等等。

兩個'EASY對於有經驗的'問題：

1）爲什麼Eclipse的讓我做靜態變量（或不編譯）？

2）該程序似乎沒有達到的功能，我把速度減半，並設置延遲到新的速度。這是爲什麼？我如何解決它？

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. 在你的榜樣，paintCount和speed有，因爲你使用的是他們沒有一個實例，從方法中，main()，它本身就是靜態是靜態的。爲了避免使它們變爲靜態，您可以將它們引用爲b.paintCount和b.speed。

2. 修改計時器的代碼需要進入paint()方法。這意味着你的Timer實例需要成爲一個實例變量，你應該在構造函數中創建並啓動計時器。順便提一下，這些更改還要求paintCount和speed也被設置爲「非靜態」。

您應該結束了，像這樣：

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);  
     } 
    } 
} 

Answer 2

1. 因爲你在main方法，它是靜態的，直接使用它們。
2. 我沒有看到這樣做的方法，但我在主方法中看到了一段代碼。這可能與paintCount % 25 == 0從來都不相符。調試它，或者使用一些println語句來查看paintCount的值是否超過前50-100個調用。這可能會給你你的答案。