Question

This is an excerise i have to complete for a uni course, its not a marked assignment and i could do with a bit of help. I can get the ball to appear on the screen and bounce of the sides, it doesnt matter at the moment if it falls through the bottom of the screen and i can get the paddle to appear on the screen at different times but i cant get them both to appear at the same time. Help please

Here are my classes

MainClass

package movingball;

public class Main
{
    public  static  void  main  (String []args)
    {
        MovingBall  world  =  new  MovingBall("Moving  Ball");
        world.setVisible(true);
        world.move();
    }
}

BallClass

package movingball;

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Point;

public class Ball
{
    private  final  int  RADIUS  = 10;

    private  Point  pos;
    private  Color  ballColour;
    private int yChange = 2;
    private int xChange = 1;
    private  int  height,  width;
    private int change;

    public  Ball  (int  frameWidth,  int  frameHeight)
    {
        change = 3;
        ballColour = Color.RED;
        width  = frameWidth;
        height  = frameHeight;
        pos  =  new  Point();
        pos.x  = (int)(Math.random() * (width - RADIUS)) +  RADIUS;
        pos.y  = (int)(Math.random() * (height/2 - RADIUS)) +  RADIUS;
    }

    //There are lots of ways you can updateBallState 
    //Note that the menu bar occupies some of the visible space
    public void move()
    {
        if(pos.y < RADIUS)
        {
           yChange = - yChange;
        }
        if(pos.x < RADIUS)
        {
           xChange = -xChange;
        }
        if(pos.x > width - RADIUS)
        {
           xChange = -xChange;
        }
        if(pos.y < height - RADIUS)
        {
           pos.translate(xChange, yChange);
        }
        if(pos.x < width - RADIUS)
        {
           pos.translate(xChange, yChange);
        }
    }

     public void updateBallState()
    {
        if (pos.y + change < height - 3*RADIUS)
        {
            pos.translate(0, change);
            // change++; //accelerate
        }
    }

    //This method can be called with a provided graphics context
    //to draw the ball in its current state 
    public void draw(Graphics  g)
    {
        g.setColor(ballColour);
        g.fillOval(pos.x - RADIUS,  pos.y - RADIUS,  2*RADIUS, 2*RADIUS);
    }  

    public void bounce()
    {
       yChange = -yChange;
       pos.translate(xChange, yChange);
    }

    public Point getPosition()
    {
       return pos;
    }
}

BallGame

package movingball;

import java.awt.Graphics;
import java.awt.event.*;

public  class  BallGame  extends  MovingBall
{

    private Paddle myPaddle = new Paddle(FRAME_WIDTH, FRAME_HEIGHT);


    public  BallGame(String  title)
    {
        super(title);
        addKeyListener(new KeyList());    
    }

    public void paint(Graphics g)
    {
       super.paint(g);
       myPaddle.paint(g);
       if(isContact())
       {
          myBall.bounce();
       }
       else
       {
          myPaddle.paint(g);
       }
    }

    public boolean isContact()
    {
       if (myPaddle.area().contains(myBall.getPosition()))
       {
          return true;
       }
       else
       {
          return false;
       }
    }

    public class KeyList extends KeyAdapter
    {
       public void keyPressed(KeyEvent k)
       {
          if(k.getKeyCode() == KeyEvent.VK_LEFT)
          {
             myPaddle.moveLeft();
          }
          if(k.getKeyCode() == KeyEvent.VK_RIGHT)
          {
             myPaddle.moveRight();
          }
       }
    }
}

MovingBall class

package movingball;

import java.awt.Graphics;
import javax.swing.JFrame;
import javax.swing.JPanel;

public  class  MovingBall  extends  JFrame
{
    protected  final  int  FRAME_WIDTH  = 240;
    protected  final  int  FRAME_HEIGHT  = 320;
    protected Ball myBall = new Ball(FRAME_WIDTH, FRAME_HEIGHT);

    public  MovingBall  (String  title)
    {
        super(title);

        setSize(FRAME_WIDTH,  FRAME_HEIGHT);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);     
    }

    public void paint(Graphics g)
    {
       super.paint(g);
       myBall.draw(g);  
    }

    public void move()
    {
       while(true)
       {
          myBall.move();
          repaint();
          try
          {
             Thread.sleep(50);
          }
          catch(InterruptedException e)
          {
             System.exit(0);
          }
       }
    }
}

Paddle class

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


public class Paddle
{
   private Color paddleColour = Color.GREEN;
   private int x,y;
   private int paddleWidth = 20;
   private int paddleHeight = 10;
   private int move = 5;


   /** Creates a new instance of Paddle */
   public Paddle(int frameWidth, int frameHeight)
   {

      x =(int)(Math.random()*(frameWidth - paddleWidth));
      y = frameHeight - paddleHeight;

   }

   public void moveRight()
   {
      x = x + move;
   }

   public void moveLeft()
   {
      x = x - move;
   }

   public Rectangle area()
   {
      return new Rectangle(x,y, paddleWidth, paddleHeight);
   }

   public void paint(Graphics g)
   {
      g.setColor(paddleColour);
      g.fillRect(x,y,paddleWidth, paddleHeight);
   }
}

Answer 1

Here are a couple of pointers to get you started. I have a lot of things to suggest but I’ll just say this to get you further than you are now. You want your JFrame to be double-buffered. That’s the first step. To do this, create a new buffer strategy for your JFrame after making it visible:

world.setVisible(true);
world.createBufferStrategy(2);

As for why your Paddle isn’t painting? You’re going to kick yourself. Look at this line:

MovingBall  world  =  new  MovingBall("Moving  Ball");

You’re not actually creating a BallGame, which is where the logic for painting the paddle is contained! (BallGame.paint()) Try:

BallGame world  =  new  BallGame("Moving  Ball");