/**
 * Class that represents a turtle that 
 * follows another turtle
 */
public class TurtleFollower extends Turtle
{
    /** Copy-pasted from Turtle. 
      * Constructor that takes the model display
      * @param modelDisplay the thing that displays the model
   */
  public TurtleFollower (ModelDisplay modelDisplay) 
  {
    // let the parent constructor handle it
    super(modelDisplay);
  }
  
  private Turtle myLeader;
  public void setLeader(Turtle aTurtle){
    myLeader = aTurtle;
  }
  
  public void step(){
    this.turnToFace(myLeader);
    this.forward(10);
  }
  
  public static void main(String [] args){
    World earth = new World();
    int size = 500;
    
    TurtleFollower t1 = new TurtleFollower(earth);
    t1.penUp(); t1.forward(size); t1.turnRight(); t1.forward(size);
    t1.setHeading(0); t1.penDown();
    TurtleFollower t2 = new TurtleFollower(earth);
    t2.penUp(); t2.forward(size); t2.turnLeft(); t2.forward(size);
    t2.setHeading(270); t2.penDown();
    TurtleFollower t3 = new TurtleFollower(earth);
    t3.penUp(); t3.forward(-size); t3.turnLeft(); t3.forward(size);
    t3.setHeading(180); t3.penDown();
    TurtleFollower t4 = new TurtleFollower(earth);
    t4.penUp(); t4.forward(-size); t4.turnRight(); t4.forward(size);
    t4.setHeading(90); t4.penDown();
    
    t1.setLeader(t2); t2.setLeader(t3); t3.setLeader(t4);
    t4.setLeader(t1);
    
    for (int i = 0; i < 100; i++){
      t1.step(); t2.step(); t3.step(); t4.step();
      try {Thread.sleep(300);} // See page 88 -- about 1/3 of a second
      catch(Exception e){System.err.println("Something went wrong!");}
    }
  }
}