4.6 More Classes

Go South

Write a GoFarStrat which makes a BirdBot fly three times.

We are not going to write a BirdBot class, but assume it is already written:

public class BirdBot extends StrategyLayer { 
  ...
  public void fly() { ... }
}

The following code should work:

public static void main (String[] args) {
  GoFarStrat flyFar = new GoFarStrat();
  BirdBot robin = new BirdBot(4,1,East,20, flyFar);
  flyFar.doIt(robin); // could be robin.doStrat()
}

AndThenStrat

The AndThenStrat is a Strategy that combines two strategies by doing one and then the other. See lines 5-6 in the code sample below for its construction and use.

The following sample code should cause the robot to step and then turn. The MoveOneStrat is supposed to make the robot move one step. The TurnOneStrat is supposed to mkae the robot turn to the left. You do not need to write either of those strategies; they are just here to illustrate how the AndThenStrat works.

1public static void demoAndThen() {
2  UrRobot r = new UrRobot(4,1,East,20);
3  Strategy step = new MoveOneStrat();
4  Strategy turn = new TurnOneStrat();
5  AndThenStrat combine = new AndThenStrat(step, turn);
6  combine.doIt( r );
7}

ZigStrat

We are going to make a strategy that is called ZigStrat. This strategy layers on top of another strategy that we are given and does three things:

• turnLeft()
• (the behavior from the given strategy)
• turnRight()

The following sample code should cause the robot to turn left, move three, and turn right:

public static void main (String[] args) {
  Strategy th = new MoveThreeStrat();
  ZigStrat z = new ZigStrat(th);
  BetterBot bb = new BetterBot(4,1,East,20);
  z.doIt(bb);
}

Background and Additional Information

The MoveThreeStrat extends the basic Strategy interface from the book:

public interface Strategy { 
   public void doIt(UrRobot r);
}

We will use a robot called BetterBot that has a turnRight() method. Do not write your own turnRight.

Extensions

Check to make sure your solution is still good when you add a public void skip() method to BetterBot that causes it to move two spaces forward. Make ZigStrat turn left, skip, do the other work, turn right, and skip again.