This program shows the same ball simulation with collision detection using “Rectangle” class of java.
Eg:-It works like this,
“r1.intersects(Rectangle r2)” method checks whether the r1 touches the r2.I have made special conditions for ball deflection based on the side it collides.
Class 1:Base Frame with some UI components
package ball_bounds;
import javax.swing.*;
import ball_bounds.canvas.ball;
import java.awt.*;
import java.awt.event.*;
public class base_frame extends JFrame implements ActionListener
{
canvas draw_panel;
JButton b_changebg,b_add,b_remove;
JPanel ui_panel;
base_frame()
{
super("Ball Bounds");
//our UI panel which contains gui comps
ui_panel=new JPanel();
b_changebg=new JButton("Change Background");
b_add=new JButton("Add");
b_remove=new JButton("Remove");
//add listeners
b_changebg.addActionListener(this);
b_add.addActionListener(this);
b_remove.addActionListener(this);
setLayout(new FlowLayout());
draw_panel=new canvas();
//adding to UI panel
ui_panel.add(b_changebg);
ui_panel.add(b_add);
ui_panel.add(b_remove);
//adding to our JFrame
add(draw_panel);
add(ui_panel);
setSize(540,470);
setVisible(true);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
public static void main(String[] args)
{
new base_frame();
}
public void actionPerformed(ActionEvent ae)
{
if(ae.getSource()==b_changebg)
{
draw_panel.changeBGcolor();
}
else
if(ae.getSource()==b_add)
{
//adds a ball of size 20;
draw_panel.addBall(20);
System.out.println("Added a ball");
}
else
if(ae.getSource()==b_remove)
{
draw_panel.removeBall();
System.out.println("Removed a ball");
}
}
}
Class 2:Our Drawing canvas
package ball_bounds;
import java.awt.*;
import java.awt.event.*;
import java.util.*;
import javax.swing.*;
public class canvas extends JComponent implements KeyListener,MouseMotionListener
{
//display details
private final int width=512;
private final int height=384;
boolean bg_change=false;
int color=254,incr=1;
//a ball array
ArrayList ballarray;
//my custom box
My_box b1;
canvas()
{
ballarray=new ArrayList(1);
b1=new My_box(0,0,120,20);
addKeyListener(this);
addMouseMotionListener(this);
setPreferredSize(new Dimension(width,height));
setFocusable(true);
}
//change to background color dynamically(default:white)
public void changeBGcolor()
{
if(bg_change)
{
bg_change=false;
}
else
{
bg_change=true;
}
}
//add a new ball by passing a "ball" class instance
public void addBall(int size)
{
//added to the arraylist
ballarray.add(new ball(size));
}
public void removeBall()
{
if(!ballarray.isEmpty())
{
ballarray.remove(ballarray.size()-1);
}
}
public int getBallCount()
{
return ballarray.size();
}
public void paintComponent(Graphics g)
{
super.paintComponent(g);
//fill rect
if(bg_change)
{
color=color-incr;
if(color<1)
{
incr=-1;
}
if(color>250)
{
incr=1;
}
g.setColor(new Color(color,color,color));
}
else
{
color=254;
g.setColor(Color.WHITE);
}
g.fillRect(0,0,getWidth(),getHeight());
//my box
g.setColor(Color.BLACK);
b1.drawBox(g);
try{
Thread.sleep(5);
for(ball temp_ball:ballarray)
{
//drawing the ball using "drawBall(Graphics g,boolean)".
//boolean is for displaying ball's bounding rectangle which deals with collision
temp_ball.drawBall(g,false);
//checking for collision with our movable pad
temp_ball.collision(b1);
}
repaint();//calls the paint method
}catch(Exception e)
{
System.out.println(e);
}
}
//keyboard call-back methods
public void keyPressed(KeyEvent ke)
{
if(ke.getKeyCode()==KeyEvent.VK_RIGHT)//increase x
{
b1.translate(10,0);
}
else
if(ke.getKeyCode()==KeyEvent.VK_LEFT)
{
b1.translate(-10,0);
}
}
public void keyReleased(KeyEvent ke)
{
}
public void keyTyped(KeyEvent ke)
{
}
//mouse call-back methods
public void mouseMoved(MouseEvent me)
{
//move the rectangle box too
b1.setLocation(me.getX(),me.getY());
}
public void mouseDragged(MouseEvent me)
{
}
//Ball inner-class
class ball
{
private int x_pos=0;
private int y_pos=0;
private int dir_x=1;
private int dir_y=1;
private int size=0;
ball(int size)
{
this.size=size;
}
private void calculate_direction()
{
//move the ball
x_pos=x_pos-dir_x;
y_pos=y_pos-dir_y;
//for X-direction
if(x_pos<0)
{
x_pos=0;
dir_x=-1;//incr
}
else
if(x_pos+size>getWidth())
{
dir_x=1;//decr
}
//for Y-direction
if(y_pos<0)
{
y_pos=0;
dir_y=-1;//incr
}
else
if(y_pos+size>getHeight())
{
dir_y=1;//decr
}
}
public void changeDirection_Y()
{
if(dir_y==-1)
{
dir_y=1;
}
else
{
dir_y=-1;
}
}
public void changeDirection_X()
{
if(dir_x==-1)
{
dir_x=1;
}
else
{
dir_x=-1;
}
}
public void drawBall(Graphics g,boolean bound)
{
calculate_direction();
g.setColor(Color.BLUE);
g.fillOval(x_pos,y_pos,size,size);
if(bound)
{
g.drawRect(x_pos,y_pos,size,size);
}
}
public Rectangle getRectBounds()
{
return new Rectangle(x_pos,y_pos,size,size);
}
//this method is called for all balls and checked whether it touches the rect.if so,the ball's direction gets changed accordingly.
public void collision(My_box rect)
{
//if ball collides with top/bottom part of the rect
if(this.getRectBounds().intersectsLine(rect.x,rect.y,rect.x+rect.width,rect.y) ||
this.getRectBounds().intersectsLine(rect.x,rect.y+rect.height, rect.x+rect.width,rect.y+rect.height))
{
changeDirection_Y();//reverses the direction along Y
}
//if ball collides with left/right part of the rect
if(this.getRectBounds().intersectsLine(rect.x,rect.y , rect.x,rect.y+rect.height) ||
this.getRectBounds().intersectsLine(rect.x+rect.width,rect.y , rect.x+rect.width,rect.y+rect.height))
{
changeDirection_X();//reverses the direction along X
}
}
}
}
Class 3:Our “My_box ” class.
This class extends Rectangle class.It is written in separate class just for future scalability.nothing specific
package ball_bounds;
import java.awt.*;
import java.awt.event.*;
class My_box extends Rectangle
{
//default vars
/*
* x,y,width,height
*/
My_box(int x1,int y,int width,int height)
{
super(x1,y,width,height);
}
public void drawBox(Graphics g)
{
g.setColor(Color.BLACK);
g.fillRect(x,y,width,height);
}
}
This is the Screenshot
Screenshot:
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