我如何将重力加到反弹的球上？

Question

我希望下面的代码中的球能够根据重力弹跳。此刻，它在墙壁的框架周围反弹。我正在制作愤怒的小鸟版本，因此引力是关键。我有一些想法，使用二次方来制作抛物线然后球，但我不确定具体的编码。

import java.awt.*;
import javax.swing.*;
import java.awt.event.*;

/**
* One ball bouncing inside a rectangular box. 
* All codes in one file. Poor design!
*/
// Extends JPanel, so as to override the paintComponent() for custom rendering codes. 
public class BouncingBallSimple extends JPanel {
// Container box's width and height
private final int BOX_WIDTH = 700;
private final int BOX_HEIGHT = 700;

// Ball's properties
private float ballRadius = 15; // Ball's radius
private float ballX = ballRadius + 50; // Ball's center (x, y)
private float ballY = ballRadius + 20; 
private float ballSpeedX = 60;   // Ball's speed for x and y
private float ballSpeedY = 60;

private static final int UPDATE_RATE = 30; // Number of refresh per second

/** Constructor to create the UI components and init game objects. */
public BouncingBallSimple() {
  this.setPreferredSize(new Dimension(BOX_WIDTH, BOX_HEIGHT));

  // Start the ball bouncing (in its own thread)
  Thread gameThread;
   gameThread = new Thread() {
@Override
public void run() {
  while (true) { // Execute one update step
     // Calculate the ball's new position
     ballX += ballSpeedX;
     ballY += ballSpeedY;
     // Check if the ball moves over the bounds
     // If so, adjust the position and speed.
     if (ballX - ballRadius < 0) {
        ballSpeedX = -ballSpeedX; // Reflect along normal
        ballX = ballRadius; // Re-position the ball at the edge
     } else if (ballX + ballRadius > BOX_WIDTH) {
        ballSpeedX = -ballSpeedX;
        ballX = BOX_WIDTH - ballRadius;
     }
     // May cross both x and y bounds
     if (ballY - ballRadius < 0) {
        ballSpeedY = -ballSpeedY;
        ballY = ballRadius;
     } else if (ballY + ballRadius > BOX_HEIGHT) {
        ballSpeedY = -ballSpeedY;
        ballY = BOX_HEIGHT - ballRadius;
     }
     // Refresh the display
     repaint(); // Callback paintComponent()
     // Delay for timing control and give other threads a chance
     try {
        Thread.sleep(1000 / UPDATE_RATE);  // milliseconds
     } catch (InterruptedException ex) { }
  }
}
};
  gameThread.start();  // Callback run()
}

/** Custom rendering codes for drawing the JPanel */
@Override
public void paintComponent(Graphics g) {
  super.paintComponent(g);    // Paint background

  // Draw the box
  g.setColor(Color.CYAN);
  g.fillRect(0, 0, getWidth(), getHeight());

  // Draw the ball
  g.setColor(Color.BLUE);
  g.fillOval((int) (ballX - ballRadius), (int) (ballY - ballRadius),
        (int)(2 * ballRadius), (int)(2 * ballRadius));
                    Graphics2D comp2D = (Graphics2D) g;                  
                    comp2D.drawRect(0, 645, 1365, 100);
                    comp2D.setColor(Color.GREEN);
                    comp2D.fillRect(0, 645, 1365, 100);
                    Graphics2D stand = (Graphics2D) g;
                    stand.setColor(Color.BLACK);
                    stand.fillRect(80, 575, 30, 70);
                    Graphics2D sling = (Graphics2D) g;
                    sling.drawArc(15, 570, 90, 50, 50, 250);
}

/** main program (entry point) */
public static void main(String[] args) {
  // Run GUI in the Event Dispatcher Thread (EDT) instead of main thread.
  javax.swing.SwingUtilities.invokeLater(new Runnable() {
     @Override
     public void run() {
        // Set up main window (using Swing's Jframe)
        JFrame frame = new JFrame("Angry Birds for Annie May Tion");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setContentPane(new BouncingBallSimple());
        frame.pack();
        frame.setVisible(true);
     }
  });
}
}