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POJava Bouncing Ball
 

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  1. POJava Bouncing Ball
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    <p>I am trying to write a Java application which draws multiple balls on screen which bounce off of the edges of the frame. I can successfully draw one ball. However when I add the second ball it overwrites the initial ball that I have drawn. The code is:</p> <pre><code>import java.awt.*; import javax.swing.*; import java.util.ArrayList; import java.util.List; public class Ball extends JPanel implements Runnable { List&lt;Ball&gt; balls = new ArrayList&lt;Ball&gt;(); Color color; int diameter; long delay; private int x; private int y; private int vx; private int vy; public Ball(String ballcolor, int xvelocity, int yvelocity) { if(ballcolor == "red") { color = Color.red; } else if(ballcolor == "blue") { color = Color.blue; } else if(ballcolor == "black") { color = Color.black; } else if(ballcolor == "cyan") { color = Color.cyan; } else if(ballcolor == "darkGray") { color = Color.darkGray; } else if(ballcolor == "gray") { color = Color.gray; } else if(ballcolor == "green") { color = Color.green; } else if(ballcolor == "yellow") { color = Color.yellow; } else if(ballcolor == "lightGray") { color = Color.lightGray; } else if(ballcolor == "magenta") { color = Color.magenta; } else if(ballcolor == "orange") { color = Color.orange; } else if(ballcolor == "pink") { color = Color.pink; } else if(ballcolor == "white") { color = Color.white; } diameter = 30; delay = 40; x = 1; y = 1; vx = xvelocity; vy = yvelocity; } protected void paintComponent(Graphics g) { super.paintComponent(g); Graphics2D g2 = (Graphics2D)g; g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON); g.setColor(color); g.fillOval(x,y,30,30); //adds color to circle g.setColor(Color.black); g2.drawOval(x,y,30,30); //draws circle } public void run() { while(isVisible()) { try { Thread.sleep(delay); } catch(InterruptedException e) { System.out.println("interrupted"); } move(); repaint(); } } public void move() { if(x + vx &lt; 0 || x + diameter + vx &gt; getWidth()) { vx *= -1; } if(y + vy &lt; 0 || y + diameter + vy &gt; getHeight()) { vy *= -1; } x += vx; y += vy; } private void start() { while(!isVisible()) { try { Thread.sleep(25); } catch(InterruptedException e) { System.exit(1); } } Thread thread = new Thread(this); thread.setPriority(Thread.NORM_PRIORITY); thread.start(); } public static void main(String[] args) { Ball ball1 = new Ball("red",3,2); Ball ball2 = new Ball("blue",6,2); JFrame f = new JFrame(); f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); f.getContentPane().add(ball1); f.getContentPane().add(ball2); f.setSize(400,400); f.setLocation(200,200); f.setVisible(true); new Thread(ball1).start(); new Thread(ball2).start(); } } </code></pre> <p>I wanted to create a List of balls and then cycle through drawing each of the balls but I'm still having trouble adding both balls to the Content Pane.</p> <p>Thanks for any help.</p>
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    1. COAre you allowed to change the constructor parameters for `Ball`?
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    2. COYes I just need to draw multiple bouncing balls, that's the only requirement.
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    3. COThis doesn't answer your question, but I would suggest changing the parameters of your constructor to just accept a `Color` object rather than a `String` and having to parse it with that ridiculous if-else statement. (i.e. `public Ball(Color ballColor, ...) { color = ballColor; ... }`
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