Java Reference
In-Depth Information
}
Brick combinedBrick = bricks . get (0) .add( bricks . get (1) ) ;
bounceBall (ball , combinedBrick) ;
}
public void
actionPerformed(ActionEvent e)
{
Ball newBall = ball . getVirtualBall () ;
ArrayList
<
Brick
>
bricksToBeDeleted =
new
ArrayList
<
Brick
>
() ;
for
(Brick brick : bricks)
{
if
(brick.intersects(newBall))
{
bricksToBeDeleted .add(brick) ;
}
bounceBall(ball , bricksToBeDeleted) ;
for
(Brick brick : bricksToBeDeleted)
{
bricks .remove(brick);
if
(newBall . intersects (paddle))
{
ba l l . goUp ( ) ;
if
(newBall . getX() + newBall . getWidth() / 2
<
paddle .getX() +
paddle . getWidth() / 2)
{
ball . goLeft () ;
}
else
{
ball . goRight () ;
}
}
else if
(ball.getY()
>
paddle .getY()
−
paddle . getHeight () )
{
player. killPlayer() ;
ba l l . goUp ( ) ;
}
ball .move() ;
repaint () ;
}
}
}
In the
actionPerformed
method, we first collect the bricks that intersect the virtual ball
and bounce the ball off the bricks by calling the
bounceBall
method. Note that we cannot
delete a brick inside the loop that iterates over the bricks. If we try to do so, an exception
of type
ConcurrentModificationException
will be generated. The reason is that an array
or an
ArrayList
cannot be modified while it is traversed using a for-each
for
loop. An
iterator is created while the elements are traversed and removing an element will make the
method that gets the next element in the list ambiguous.
If the virtual ball intersects a single brick, then we simply check the location of the ball
relative to the brick and change the trajectory of the ball accordingly. This is done in the
first
bounceBall
method. If there are two bricks that intersect the virtual ball, then we
merge the bricks and call the first
bounceBall
method again. This case only happens when
the bricks are adjacent horizontally or vertically. Note that it is possible that a ball is both
above and to the right of a brick. In this case, both the horizontal and vertical direction of
the ball will be changed. The class also introduced the
createBricks
and
getRandomColor
methods, which were described in detail in Chapter 9.
We have also changed the
paintComponent
method. Now it checks if the game has
started and the number of bricks is equal to zero. If this is the case, then this means that
all the bricks have been destroyed and we have won the game. An appropriate message is
