Java Reference
In-Depth Information
if
(getY()+getHeight ()+dy
>
panel . getHeight ())
{
dy =
−
1;
super
.move(dx, dy);
}
}
The size of the ball and its initial coordinates are defined as constants. The constructor
of the ball creates a ball by calling the constructor of the
BreakoutShape
class. A ball will
be moved by changing its
x
and
y
coordinates. The ball should move with constant speed.
Therefore, we will move the ball by adding
dx
and
dy
to its
x
and
y
coordinates, respectively.
Therefore, (
x
+
dx
,
y
+
dy
) are the new coordinates of the ball. Note that the constructor of
the
Ball
class takes as input the panel in which the ball will move. The ball needs to know
about the panel so that it can bounce off the panel's walls.
Let us examine the
move
method in greater detail. Before the ball is moved, the value
of the variables
dx
of
dy
may need to be changed. For example, if
x+dx <0
, this means that
the new value of
x
will be smaller than 0 and the value of
dx
needs to be made positive.
Similarly, if
x+ballWidh+dx > panelWidth
, then the new value of
x
will make the ball go
over the right corner of the screen and the value of
dx
needs to be made
−
1. The value of
dy
is computed similarly.
Let us see how our code works so far. Here is the main class.
public class
Breakout
{
public static void
main(String [] args)
{
BreakoutFrame frame =
new
BreakoutFrame () ;
frame. setVisible(
true
);
}
}
The class simply creates the game window and makes it visible. Here is the code for the
game window.
import
javax . swing .
∗
;
import
java .awt. event .
∗
;
{
public class
BreakoutFrame
extends
JFrame
private static final int
HEIGHT = 600;
private static final int
WIDTH = 488;
private
BreakoutPanel panel =
new
BreakoutPanel () ;
public
BreakoutFrame ()
{
setDefaultCloseOperation(JFrame.DISPOSEON CLOSE) ;
setLocation(100,100) ;
setSize(WIDTH, HEIGHT);
add(panel) ;
setResizable(
false
);
}
}
The
setDefaultCloseOperation
method assures that the window will be disposed of
when the close button is pressed. The width and the height of the window are set, where the
two numbers are defined as constants so that the dimensions of the window can be easily
changed. Finally, the panel is added to the window and the window is made non-resizable.
Let us next examine the code for the panel.
