CS 40 Fall 2009 Homework 3

1. Make a world containing a helicopter (in vehicles folder), a control tower (buildings folder), and a light house (beach folder). Add a method circleAround that has a parameter of type Object named target. The method causes the helicopter to circle around the target. Use this strategy for circling:

• Make the helicopter face the target
• helicopter.move(helicopter.distance(target) - 10) toward target asSeenBy helicopter
• Make the helicopter turn 90 degrees
• In a loop, make the helicopter move a bit, turn a bit, move a bit, turn a bit, so that it eventually makes a complete circle. I did this by trial and error. Looping 100 times, turning 0.01 revolution each time, moving forward by 0.5 meters seemed to work for me. I put the turn and move in a "Do together", it looks much better. Changing the duration to make each of these commands quick (say .1 second) is also good if you don't want to wait 100 seconds for one time around the lighthouse. Of course, you could use math to figure out the values for turning and moving if you prefer...

In World.my_first_method, first have the helicopter call circleAround(lighthouse), then have the helicopter call circleAround(controlTower).

20 points.

Grading criteria

a) Does the circleAround method have a parameter of type target?

b) Does the code of the circleAround method always refer to target, never to the lighthouse or controlTower?

c) Does the circling work?

d) Does my_first_method contain two calls to the circleAround method?

2. Make a class CirclingCopter, a helicopter with the circleAround method. (If you were unable to do part 1, just implement the method by having the helicopter say "I wish I could fly in a circle." You'll still get all points for this part.)

Your CirclingCopter should have some color or texture that makes it look different from the regular helicopter.

Make a world with two instances of that class, and two different buildings. Have them simultaneously circle different buildings, and after once around their respective buildings, have one of the helicopters join the other, with both now circling a single building (at different heights).

15 points

Grading criteria

a) Is there a class CirclingCopter in this world?

b) Are there two instances of the class in this world?

c) Does my_first_method contain two calls to the circleAround method?

Put two attachments, helicopter1.a2w and helicopter2.a2w into an email to taylor@cs.sjsu.edu. Make the subject: CS40 Homework 3 Firstname Lastname, where your name is filled in for firstname and lastname. Due date: 9/27. Test on 9/30.