Lecture 11: More Repetition

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Lecture 11 More Repetition Talking to
ActiveObjects
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Finally -- Pong!

• Recall the Pong game from last time
• The balls move around, but whats the big deal?
• Their motion is tracked in 2 directions
• X direction
• Y direction
• We take time into account when moving the balls
• Constant motion with respect to time

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From last time run() in MovingBall
public void run() // used to record times
and compute time between moves double
elapsedTime double lastTime
System.currentTimeMillis() while
(ball.getY() lt offScreen) elapsedTime
System.currentTimeMillis() - lastTime
ball.move(xspeedelapsedTime,yspeedelapsedTime)
if ( ball.getX() lt bleft ball.getX()
gt bright ) xspeed -xspeed
if ( ball.getY() lt btop )
yspeed initYspeed else if (
ball.overlaps(paddle) ) yspeed
-initYspeed lastTime
System.currentTimeMillis()
pause(PAUSETIME) ball.removeFromCanvas()

• Well go through this loop one more time
• Note use of System.currentTimeMillis() to get the
  time
• pause() takes at least as many milliseconds as
  you give it
• So we have to ask the system how many ms really
  elapsed
• We move the ball as far as it would have moved in
  that much time

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One more thing

• Remember the constructor for MovingBall?
• Notice that we passed the paddle to the Ball
• Why does the Ball know about the paddle and not
  vice versa?

public MovingBall(DrawingCanvas aCanvas,
Filled Rect thePaddle, FramedRect boundary)
paddle thePaddle //etc
start()
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One more thing

• Why does the MovingBall know about the paddle and
  not vice versa?
• The MovingBall is the active object
• Its constantly running a while loop, and can
  check whether it overlaps the paddle all the time
• Paddle is just a FramedRect
• Even if we tried to check for overlap in
  onMouseMove(), what if the user doesnt move the
  mouse?
• Passive object might not check frequently enough
  for a game like this!

public MovingBall(DrawingCanvas aCanvas,
Filled Rect thePaddle, FramedRect boundary)
paddle thePaddle //etc
start()
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More on loops Nested while loops

• Take a look at the example program to draw
  American Flags
• Only draws with 48 stars
• Todays flag is harder, so we stuck with this one
• Uses two loops to draw the stars
• Look at the drawStars method in the Flag class
• 2 nested loops

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More on loops Nested while loops

• Look at the drawStars method in the Flag class
• 2 nested loops
• Outer loop iterates over rows
• Inner loop iterates over columns

while (row lt NUM_ROWS_STARS) col 0
x point.getX()OFFSET while (col lt
NUM_COLS_STARS) new FilledOval(
x, y, STAR_DIAM, STAR_DIAM,canvas
).setColor(Color.white) col
x x STAR_JUMP y y
STAR_JUMP row
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Some other new things

• operator
• We can use to increment a numbers value by
  one
• This is the same as just saying
• Its shorter, so programmers like it.
• You can use whichever you want, but this is more
  common.

col
col col 1
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Some other new things

• Private methods
• Here are their headers
• These arent designed to be used outside of the
  Flag class, so theyre private
• These are only called inside of Flag
• They just let us break the work up into easy to
  manage pieces
• drawStripes is particularly useful b/c it lets us
  draw different kinds of stripes
• We can set the width and the number of stripes on
  each call

private void drawStars(Location point) private
void drawStripes( double x, double y, double
width, int numStripes )
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More loops drawing a basket
// top of the basket new Line(x, y,
xBASKET_SIZE, y, canvas) // bottom of
the basket new Line(xINSET,
yBASKET_HEIGHT, xBASKET_SIZE-INSET,
yBASKET_HEIGHT, canvas) topLineX x
botLineX xINSET while ( topLineX lt
xBASKET_SIZE) new Line(topLineX, y,
botLineX, yBASKET_HEIGHT, canvas)
topLineX topLineX LINESEP botLineX
botLineX LINESEP(BASKET_SIZE-2.0INSET)/BASKET_
SIZE

• Look at Laundry Basket example program
• Draws (sort of) a laundry basket
• Draws almost-vertical lines from left to right
• Top x coord is changing faster than bottom x

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More loops drawing a scarf

• This will be a lot like drawing the American Flag
• Draws a bunch of circles, as shown, but theyre
  interlocking
• Well put this together piece by piece.

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First draw one row

• Well start by drawing one row of the scarf
• This is pretty easy -- just one loop!

// draws a scarf with upper left at point of
click public void onMouseClick( Location
point ) double x point.getX()
double y point.getY() // x and y
positions of the next "stitch"
int numCols 0 while (numCols
lt SCARF_WIDTH) new FramedOval(x, y,
DIAMETER, DIAMETER,
canvas).setColor(Color.green) x x
X_DISP numCols numCols 1

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First draw one row
// draws a scarf with upper left at point of
click public void onMouseClick( Location
point ) double x point.getX()
double y point.getY() // x and y
positions of the next "stitch"
int numCols 0 while (numCols
lt SCARF_WIDTH) new FramedOval(x, y,
DIAMETER, DIAMETER,
canvas).setColor(Color.green) x x
X_DISP numCols numCols 1

• Each time through
• Increase the value of x
• increase numCols

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Now draw more than one
// draws a scarf with upper left at point of
click public void onMouseClick( Location
point ) double x point.getX()
double y point.getY() // x and y
positions of the next "stitch"
int numCols 0 while (numCols
lt SCARF_WIDTH) new FramedOval(x, y,
DIAMETER, DIAMETER,
canvas).setColor(Color.green) x x
X_DISP numCols numCols 1

• Want to change this so it draws multiple rows
• Each time we start a row, we need to
• Reset value of x so that we draw starting at the
  beginning of the row
• Increase the value of y so that we dont draw
  rows on top of each other
• Reset numCols so that it keeps the correct count
• Increment numRows each time through

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Final version

• New code is labeled with //new!
• Recall the 4 things we needed to do
• Reset value of x so that we draw starting at the
  beginning of the row
• Increase the value of y so that we dont draw
  rows on top of each other
• Reset numCols so that it keeps the correct count
• Increment numRows each time through

// draws a scarf with upper left at point of
click public void onMouseClick( Location
point ) // x and y positions of the
next "stitch" double x point.getX()
double y point.getY()
int numRows 0 // new!
int numCols 0 while (numRows
lt SCARF_T) // new! while
(numCols lt SCARF_WIDTH) new
FramedOval( x, y, DIAMETER,
DIAMETER, canvas
).setColor(Color.green) x x
X_DISP numCols numCols 1
x point.getX()
// new! y y Y_DISP
// new! numCols 0
// new! numRows numRows 1 //
new!
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Now try this

• Modify the code so that
• First row only has one circle
• Second row has two circles
• Third row has three circles
• Etc
• Well do this in class

// draws a scarf with upper left at point of
click public void onMouseClick( Location
point ) // x and y positions of the
next "stitch" double x point.getX()
double y point.getY()
int numRows 0 // new!
int numCols 0 while (numRows
lt SCARF_T) // new! while
(numCols lt SCARF_WIDTH) new
FramedOval( x, y, DIAMETER,
DIAMETER, canvas
).setColor(Color.green) x x
X_DISP numCols numCols 1
x point.getX()
// new! y y Y_DISP
// new! numCols 0
// new! numRows numRows 1 //
new!
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New topic Talking to Active Objects

• Active Objects can have methods just like other
  objects
• Recall last time when I was saying you could make
  a wind class that moved clouds around in our
  snow program
• Well revisit our basketball program, but this
  time the balls will dribble
• Well have a Dribbler class that moves them up
  and down

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Dribbling

• How would you describe dribbling?
• We could use a loop like in Pong
• Move the ball by some amount
• Use a positive value sometimes
• Use a negative value other times
• Switch the value to switch directions
• Seems a little complicated how about something
  more natural?

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Dribbling

• If we were to say this in English, we might say
  something like
• Hey, thats more natural (hopefully)
• Theres an outer loop (for while carrying)
• And two nested loops for the slowly move parts

while were carrying the ball Slowly move
the ball up a few times Slowly move the
ball down a few times
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Dribbling

• Heres the actual code to dribble the ball
• This is in the run() method of our ActiveObject
  Dribbler
• Notice that theres a boolean variable called
  moving that controls the loop
• We could make the ball stop if we could change
  the value of that boolean

while ( moving ) int moveCount
// make ball bounce down moveCount
0 while ( moveCount lt MOVES moving)
ball.move(0, MOVESIZE)
pause( DELAY ) moveCount
bounce.play()
// make ball bounce up moveCount 0
while ( moveCount lt MOVES moving)
ball.move(0,-MOVESIZE)
pause( DELAY ) moveCount

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Stopping the dribbling

• We can add another method to the Dribbler class
• This will change the value of moving to false
• If its called while the run() method is going
  on, then the run method will stop executing when
  it checks its condition
• The dribblers run method will then finish, and
  the dribbler thread will die

public void stopDribbling() moving false
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Calling our new method

• We can call stopDribbling() from the Basketball
  class (the game, not the ball)
• When the user clicks the mouse, well do this

public void onMousePress(Location point)
lastMouse point if ( ballInPlay null
) if ( leftBall.contains( point ) )
ballInPlay leftBall else
if ( rightBall.contains( point ) )
ballInPlay rightBall else
player.stopDribbling()
player null ballInPlay.moveTo(
point.getX() - BALLSIZE/2,
point.getY() - BALLSIZE/2)