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This chapter has not
had any significant translation yet.
A number of more challenging
projects for you to solve. [[Some of these may turn into examples in the book,
and so at some point might disappear from here]]
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First, create a Blackboard (cite
reference) which is an object on which anyone may record information. This
particular blackboard draws a maze, and is used as information comes back about
the structure of a maze from the rats that are investigating it.
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Now create the maze itself. Like a real
maze, this object reveals very little information about itself — given a
coordinate, it will tell you whether there are walls or spaces in the four
directions immediately surrounding that coordinate, but no more. For starters,
read the maze in from a text file but consider hunting on the internet for a
maze-generating algorithm. In any event, the result should be an object that,
given a maze coordinate, will report walls and spaces around that coordinate.
Also, you must be able to ask it for an entry point to the maze.
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Finally, create the maze-investigating
Rat class. Each rat can communicate with both the blackboard to give the
current information and the maze to request new information based on the current
position of the rat. However, each time a rat reaches a decision point where the
maze branches, it creates a new rat to go down each of the branches. Each rat is
driven by its own thread. When a rat reaches a dead end, it terminates itself
after reporting the results of its final investigation to the blackboard.
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The goal is to completely map the maze,
but you must also determine whether the end condition will be naturally found or
whether the blackboard must be responsible for the decision.
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An example implementation by Jeremy
Meyer:
# c13:Maze.py
class Maze(Canvas):
private Vector lines # a line is a char array
private int width = -1
private int height = -1
public static void main (String [] args)
throws IOException:
if (args.length < 1):
print “Enter filename“
System.exit(0)
Maze m = Maze()
m.load(args[0])
Frame f = Frame()
f.setSize(m.width*20, m.height*20)
f.add(m)
Rat r = Rat(m, 0, 0)
f.setVisible(1)
def __init__(self):
lines = Vector()
setBackground(Color.lightGray)
synchronized public boolean
isEmptyXY(int x, int y):
if (x < 0) x += width
if (y < 0) y += height
# Use mod arithmetic to bring rat in line:
byte[] by =
(byte[])(lines.elementAt(y%height))
return by[x%width]==' '
synchronized public void
setXY(int x, int y, byte newByte):
if (x < 0) x += width
if (y < 0) y += height
byte[] by =
(byte[])(lines.elementAt(y%height))
by[x%width] = newByte
repaint()
public void
load(String filename) throws IOException:
String currentLine = null
BufferedReader br = BufferedReader(
FileReader(filename))
for(currentLine = br.readLine()
currentLine != null
currentLine = br.readLine()) :
lines.addElement(currentLine.getBytes())
if(width < 0 ||
currentLine.getBytes().length > width)
width = currentLine.getBytes().length
height = len(lines)
br.close()
def update(self, Graphics g): paint(g)
public void paint (Graphics g):
int canvasHeight = self.getBounds().height
int canvasWidth = self.getBounds().width
if (height < 1 || width < 1)
return # nothing to do
int width =
((byte[])(lines.elementAt(0))).length
for (int y = 0 y < len(lines) y++):
byte[] b
b = (byte[])(lines.elementAt(y))
for (int x = 0 x < width x++):
switch(b[x]):
case ' ': # empty part of maze
g.setColor(Color.lightGray)
g.fillRect(
x*(canvasWidth/width),
y*(canvasHeight/height),
canvasWidth/width,
canvasHeight/height)
break
case '*': # a wall
g.setColor(Color.darkGray)
g.fillRect(
x*(canvasWidth/width),
y*(canvasHeight/height),
(canvasWidth/width)-1,
(canvasHeight/height)-1)
break
default: # must be rat
g.setColor(Color.red)
g.fillOval(x*(canvasWidth/width),
y*(canvasHeight/height),
canvasWidth/width,
canvasHeight/height)
break
# :~# c13:Rat.py
class Rat:
static int ratCount = 0
private Maze prison
private int vertDir = 0
private int horizDir = 0
private int x,y
private int myRatNo = 0
def __init__(self, Maze maze, int xStart, int yStart):
myRatNo = ratCount++
print ("Rat no." + myRatNo +
" ready to scurry.")
prison = maze
x = xStart
y = yStart
prison.setXY(x,y, (byte)'R')
Thread():
def run(self){ scurry()
.start()
def scurry(self):
# Try and maintain direction if possible.
# Horizontal backward
boolean ratCanMove = 1
while(ratCanMove):
ratCanMove = 0
# South
if (prison.isEmptyXY(x, y + 1)):
vertDir = 1 horizDir = 0
ratCanMove = 1
# North
if (prison.isEmptyXY(x, y - 1))
if (ratCanMove)
Rat(prison, x, y-1)
# Rat can move already, so give
# this choice to the next rat.
else:
vertDir = -1 horizDir = 0
ratCanMove = 1
# West
if (prison.isEmptyXY(x-1, y))
if (ratCanMove)
Rat(prison, x-1, y)
# Rat can move already, so give
# this choice to the next rat.
else:
vertDir = 0 horizDir = -1
ratCanMove = 1
# East
if (prison.isEmptyXY(x+1, y))
if (ratCanMove)
Rat(prison, x+1, y)
# Rat can move already, so give
# this choice to the next rat.
else:
vertDir = 0 horizDir = 1
ratCanMove = 1
if (ratCanMove): # Move original rat.
x += horizDir
y += vertDir
prison.setXY(x,y,(byte)'R')
# If not then the rat will die.
try:
Thread.sleep(2000)
catch(InterruptedException ie):
print ("Rat no." + myRatNo +
" can't move..dying..aarrgggh.")
# :~The maze initialization file:
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#:! c13:Amaze.txt
* ** * * ** *
*** * ******* * ****
*** ***
***** ********** *****
* * * * ** ** * * * ** *
* * * * ** * * * * **
* ** * **
* ** * ** * ** * **
*** * *** ***** * *** **
* * * * * *
* ** * * * ** * *
# :~A discussion of algorithms to create
mazes as well as Java source code to implement them:
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A discussion of algorithms for collision
detection and other individual/group moving behavior for autonomous physical
objects:
Create a pair of decorators for I/O
Readers and Writers that encode (for the Writer decorator) and decode (for the
reader decorator)
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