如何将对象添加到 JPanel 中

Question

我正在尝试将球添加到 JPanel 中，但是我不确定如何执行此操作下面是我目前拥有的用于将球添加到 JPanel 中的代码。我正在尝试在屏幕上的随机位置添加多个球。第一个按预期出现，但除此之外没有出现在屏幕上。

球class;

public class Ball extends Component {

public static double ballX = rand.nextInt(500) + 40;
public static double ballY = rand.nextInt(300) + 10;
public static Ball[] balls = new Ball[20];

public Ball() {

}

public void draw(Graphics g2) {            
    Color color = new Color(r, g, b);
    g2.setColor(color);
    g2.fillOval((int) ballX, (int) ballY, 30, 30);
}
}

尝试将球添加到 JPanel 的方法；

public class BallFrames extends JFrame {

/* creates static varibles privite for use withing class and public for 
   use out side of the class */
public static final JPanel controlPanel = new JPanel(new FlowLayout(FlowLayout.LEFT));
public static final JPanel ballPanel = new JPanel();
public static JButton button;
public static JPanel displayPanel = new JPanel(new BorderLayout());
private static int FRAME_WIDTH = 600;
private static int FRAME_HEIGHT = 600;

/**
 * constructor called method to create the components
 */
public BallFrames() {
    setSize(FRAME_WIDTH,FRAME_HEIGHT);
    createComponents(); // creates all compononents
}

/*
* calls helper methods to create all of the componanats needed
 */
private void createComponents() {
    ActionListener listener = new BallListener(); 
    createPanel(); // creates a panel
    createButtons(listener); // Creates a button
    createSlider();
}

/**
 * method to create panels
 */
public void createPanel() {
    BallComponent component = new BallComponent(); // creates a new BallCompoenet
    displayPanel.add(component, BorderLayout.CENTER); 
    displayPanel.add(controlPanel, BorderLayout.SOUTH); // adds thecontrol panel
    add(displayPanel); // adds the dice to the JFrame   
}

public static void addBall() throws InterruptedException {
   Ball.balls[BallListener.balls] = new Ball();
   System.out.println(BallListener.balls); // testing
   ballPanel.add(Ball.balls[BallListener.balls]);
   // ballPanel.add(ball);
    Runnable r = new BallRunnable();
    Thread t = new Thread(r);
    t.start();
    t.join();
    ballPanel.repaint();
}

我是怎么画的；

public class BallComponent extends JComponent {

/**
 * calls paintComponenet to render images on the screen
 *
 * @param g
 */
@Override
public void paintComponent(Graphics g) {
    int delay = 1000;
    super.paintComponent(g);        // call to super
    Graphics2D g2 = (Graphics2D) g; // recover the graphic     

    TimerListener listener = new TimerListener();
    Timer t = new Timer(delay, listener);     

    if (BallListener.gameOn == true) {
        for(int i = 0; i < BallListener.balls; i++){           
            Ball.balls[i].draw(g2);
        }

    BallFrames.displayPanel.repaint();
}
}

ActionListener for the buttons;

public class BallListener implements ActionListener {

public static boolean gameOn = false;
public static int balls = 0;

/**
 * gets the which button has been pressed and responds appriately
 *
 * @param event based on the event it will preform selected actions
 */
@Override
public void actionPerformed(ActionEvent event) {
    String action = event.getActionCommand();

    switch (action) {
        case "start":
            gameOn = true;

             {
                try {
                    BallFrames.addBall();
                } catch (InterruptedException ex) {
                    Logger.getLogger(BallListener.class.getName()).log(Level.SEVERE, null, ex);
                }
                balls++;
            }
            BallFrames.displayPanel.repaint();
            break;
        case "pause":

            break;
    }
}

球可运行；

public class BallRunnable implements Runnable {

private static Random rand = new Random();
public static boolean goLeft = true;
public static boolean goRight = false;
public static boolean goUp = false;
public static boolean goDown = false;
public static boolean diagonalUp = false;
public static boolean diagonalDown = false;
public static double speed = 0.2f;

public BallRunnable() {

}

public void run() {
    boundsCheckY1();
    boundsCheckX1();
    boundsCheckY2();
    boundsCheckX2();
}

public void boundsCheckX1() {
    int temp;

    if (Ball.ballX < 1) {
        temp = rand.nextInt(5) + 1;

       if(temp == 1) {
          goRight = true;
          goLeft = false;
          goUp = false;
          goDown = false;
          diagonalUp = false;
          diagonalDown = false;
       } else if (temp == 2) {
          goRight = true;
          goUp = true;
          goDown = false;
          goLeft = false;
          diagonalUp = false;
          diagonalDown = false;
       } else if (temp == 3) {
          goRight = true;
          goUp = false;
          goDown = true;
          goLeft = false;
          diagonalUp = false;
          diagonalDown = false;
       } else if (temp == 4) {
          goRight = true;
          goUp = false;
          goDown = false;
          goLeft = false;
          diagonalUp = true;
          diagonalDown = false;
       } else if (temp == 5) {
          goRight = true;
          goUp = false;
          goDown = false;
          goLeft = false;
          diagonalUp = false;
          diagonalDown = true;
       } 
    }
}

public void boundsCheckY1(){
    int temp;

    if (Ball.ballY < 1) {
       temp = rand.nextInt(5) + 1;

       if(temp == 1) {
          goRight = false;
          goLeft = false;
          goUp = false;
          goDown = true;
          diagonalUp = false;
          diagonalDown = false;
       } else if (temp == 2) {
          goRight = false;
          goUp = false;
          goDown = true;
          goLeft = true;
          diagonalUp = false;
          diagonalDown = false;
       } else if (temp == 3) {
          goRight = true;
          goUp = false;
          goDown = true;
          goLeft = false;
          diagonalUp = false;
          diagonalDown = false;
       } else if (temp == 4) {
          goRight = true;
          goUp = false;
          goDown = true;
          goLeft = false;
          diagonalUp = false;
          diagonalDown = true;
       } else if (temp == 5) {
          goRight = false;
          goUp = false;
          goDown = true;
          goLeft = true;
          diagonalUp = false;
          diagonalDown = true;
       }
    }
}

public void boundsCheckX2 () {
    int temp;

    if (Ball.ballX > 559) {
       temp = rand.nextInt(5) + 1;

      if(temp == 1) {
          goRight = false;
          goLeft = true;
          goUp = false;
          goDown = false;
          diagonalUp = false;
          diagonalDown = false;
       } else if (temp == 2) {
          goRight = false;
          goUp = true;
          goDown = false;
          goLeft = true;
          diagonalUp = false;
          diagonalDown = false;
       } else if (temp == 3) {
          goRight = false;
          goUp = false;
          goDown = true;
          goLeft = true;
          diagonalUp = false;
          diagonalDown = false;
       } else if (temp == 4) {
          goRight = false;
          goUp = false;
          goDown = false;
          goLeft = true;
          diagonalUp = true;
          diagonalDown = false;
       } else if (temp == 5) {
          goRight = false;
          goUp = false;
          goDown = false;
          goLeft = true;
          diagonalUp = false;
          diagonalDown = true;
       } 
    }
}

public void boundsCheckY2() {
    int temp;

     if (Ball.ballY > 470) {
       temp = rand.nextInt(5) + 1;

       if(temp == 1) {
          goRight = false;
          goLeft = false;
          goUp = true;
          goDown = false;
          diagonalUp = false;
          diagonalDown = false;
       } else if (temp == 2) {
          goRight = false;
          goUp = true;
          goDown = false;
          goLeft = true;
          diagonalUp = false;
          diagonalDown = false;
       } else if (temp == 3) {
          goRight = true;
          goUp = true;
          goDown = false;
          goLeft = false;
          diagonalUp = false;
          diagonalDown = false;
       } else if (temp == 4) {
          goRight = true;
          goUp = true;
          goDown = false;
          goLeft = false;
          diagonalUp = true;
          diagonalDown = false;
       } else if (temp == 5) {
          goRight = false;
          goUp = true;
          goDown = false;
          goLeft = true;
          diagonalUp = true;
          diagonalDown = false;
       }
    }
}

}

观众class;

public class BallViewer {

/**
 * creates the main frame
 *
 * @param args
 */
public static void main(String[] args) throws InterruptedException {
    java.awt.EventQueue.invokeLater(new Runnable() {
        public void run() {
            try {
                for (LookAndFeelInfo info : UIManager.getInstalledLookAndFeels()) {
                    if ("Nimbus".equals(info.getName())) {
                        UIManager.setLookAndFeel(info.getClassName());
                        break;
                    }
                }
            } catch (Exception e) {
                // If Nimbus is not available, you can set the GUI to another look and feel.
            }
            // new BallFrames().setVisible(true);
            JFrame frame = new BallFrames(); // creates new JFrame     
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.setTitle("Multi-Treaded Balls");// Sets the Title       
            frame.setVisible(true); // Makes the frame visible
            frame.setResizable(false);
        }
    });
}

}

定时器监听器； public class TimerListener 实现 ActionListener {

@Override
public void actionPerformed(ActionEvent event) {
    String action = event.getActionCommand();

    try {
        movement();
    } catch (InterruptedException ex) {
        Logger.getLogger(TimerListener.class.getName()).log(Level.SEVERE, null, ex);
    }

}
 public void movement() throws InterruptedException {
    if(goLeft == true) {       
        Ball.ballX -= speed;                     
    }
    if(goRight == true) {
        Ball.ballX += speed;           
    }
    if(goUp == true) {
        Ball.ballY -= speed;                         
    }
    if(goDown == true) {
        Ball.ballY += speed;            
    }
    if(diagonalUp == true) {
        Ball.ballY += speed / 2;              
    }
    if(diagonalDown == true) {
        Ball.ballY -= speed / 2;         
    }

}

}

我希望能够在给定时间在屏幕上添加多个球，它也像第一个球一样四处移动。

Answer 1

绘画代码仅用于绘画。

你永远不应该 create/start 绘画方法中的计时器。摆脱所有这些代码。

永远不要调用 repaint()，这会导致无限循环。

此外，删除所有动画代码。您的首要任务是在面板上绘制多个球。一旦你开始工作，你就会担心尝试做动画。

无需扩展 JComponent，因为您 class 不是组件。那就是您永远不会将组件添加到面板中。您所做的就是在另一个 class.

中绘制对象

因此您的 BallComponent class（这是一个组件）需要有一个 ArrayList 来跟踪您要绘制的球对象。所以你需要一个方法来将球对象添加到这个 ArrayList 中。然后 paintComponent() 方法简单地遍历列表并绘制所有球。

查看 Custom Painting Approaches 中的 DrawOnComponent 示例。

Answer 2

您对球的定义 class 表现符合预期：

public class Ball extends Component {

public static double ballX = rand.nextInt(500) + 40;
public static double ballY = rand.nextInt(300) + 10;
public static Ball[] balls = new Ball[20];

public Ball() {

}

public void draw(Graphics g2) {            
    Color color = new Color(r, g, b);
    g2.setColor(color);
    g2.fillOval((int) ballX, (int) ballY, 30, 30);
}
}

所有 static 字段在 class 的所有实例之间共享。这就是 static 的意思。所有 Ball 都具有相同的 ballX 和 ballY 坐标。

您要查找的是属于每个单独实例的非static 字段。每次制作新球时，您还必须初始化这些字段。 static 字段仅在加载 class 时初始化一次。我还建议进行一些更改：

如果你的x坐标和y坐标只属于一个球，最好做成private。
扩展 JComponent 而不是 Component，因为您显然在此处使用了 swing。
实施 paintComponent 而不是 draw。如果没有别的，它将使您的绘图代码需要更少的维护。

这是 class 的一个版本，应该会更好一些：

public class Ball extends JComponent
{

    private double ballX;
    private double ballY;
    public static Ball[] balls = new Ball[20];

    public Ball()
    {
        ballX = rand.nextInt(500) + 40;
        ballY = rand.nextInt(300) + 10;
    }

    public void paintComponent(Graphics g2)
    {
        Color color = new Color(r, g, b);
        g2.setColor(color);
        g2.fillOval((int) ballX, (int) ballY, 30, 30);
    }
}

如何将对象添加到 JPanel 中

How to add a object into a JPanel

java

user-interface

swing

multithreading

runnable