Wednesday, October 18, 2000
Part 1 -- JEM Diagrams for Recursive methods
Below are the declarations for two classes: a
ThrowerWorld class that is a subclass of
BuggleWorld and a ThrowerBuggle class that
is a subclass of Buggle.
// a BuggleWorld in which Buggles throw Bagels
public class ThrowerWorld extends BuggleWorld {
public void run () {
ThrowerBuggle tara = new ThrowerBuggle();
tara.throwBagel(3);
}
}
class ThrowerBuggle extends Buggle {
public void throwBagel (int distance) {
if (distance == 0) {
dropBagel();
} else {
forward();
throwBagel(distance - 1);
backward();
}
}
}
Task 1a) Draw the result (in a ThrowerWorld
grid) of asking tara to throw bagels at distances of 0,
1, 2, 3, 4, and 5. Use a different grid for each distance. The size
of the grid doesn't matter (just make it large enough so the buggle
doesn't run into walls). When given recursive code, it is usually a
good idea to draw on paper a couple of instances of running the code
beginning with the easiest case and working up.
Task 1b) Draw a Java Execution Model diagram that shows all
of the execution frames created by invoking the run()
method on an instance of the ThrowerWorld class. Your
diagram should depict the point in time when the invocation of
run() returns. Although Java can discard an execution
frame when control returns from it, you should not discard any frames
when drawing your diagram.
Most of the programming problems for this lab take place in extensions of TurtleWorld. The code is in the lab5_programs folder within the /usr/users/cs111/download directory on nike.wellesley.edu. The problems are arranged in order of difficulty with the easiest problem first. The last problem is a BuggleWorld recursion problem.
Working samples of the above worlds are available in the Test folder which is included in the lab5_programs folder.