Greenfoot Video Tutorials

Part I

Movement Tutorial I

Part II

A closer look at the Wombat Class's Code

Below is the code for the Wombat class. To see this code. Right-click over the Wombat Icon and choose "Open editor".

You then see code similar to the picture below.

Find the move() method in your wombat class. Here is some code that I added to the move() method.


In the text area below is all of the code for the "modified" Wombat Class. Copy all of the code from the text area below into your Wombat class. Then put a new wombat on the stage and run the program.
import greenfoot.*; // (World, Actor, GreenfootImage, and Greenfoot) import java.util.List; import java.util.ArrayList; /** * Wombat. A Wombat moves forward until it can't do so anymore, at * which point it turns left. If a wombat finds a leaf, it eats it. * * @author Michael Kolling * @version 1.0.1 */ public class Wombat extends Actor { private static final int EAST = 0; private static final int WEST = 1; private static final int NORTH = 2; private static final int SOUTH = 3; private int direction; private int leavesEaten; int numberOfStepsTaken = 0; public Wombat() { setDirection(NORTH); leavesEaten = 0; } public void act() { if (Greenfoot.isKeyDown("right") ) System.out.println("Right Key Is down"); if(foundLeaf()) { eatLeaf(); } else if(canMove()) { move(); } else { turnLeft(); } } // Check whether there is a leaf in the same cell as we are. public boolean foundLeaf() { Actor leaf = getOneObjectAtOffset(0, 0, Leaf.class); if(leaf != null) { return true; } else { return false; } } /** * Eat a leaf. */ public void eatLeaf() { Actor leaf = getOneObjectAtOffset(0, 0, Leaf.class); if(leaf != null) { // eat the leaf... getWorld().removeObject(leaf); leavesEaten = leavesEaten + 1; } } /** * Move one cell forward in the current direction. */ public void move() { if (!canMove()) { return; } numberOfStepsTaken++; if(numberOfStepsTaken > 10) { return ; } else{ System.out.println("Number of steps from move() method " + numberOfStepsTaken); } switch(direction) { case SOUTH : setLocation(getX(), getY() + 1); break; case EAST : setLocation(getX() + 1, getY()); break; case NORTH : setLocation(getX(), getY() - 1); break; case WEST : setLocation(getX() - 1, getY()); break; } } /** * Test if we can move forward. Return true if we can, false otherwise. */ public boolean canMove() { World myWorld = getWorld(); int x = getX(); int y = getY(); switch(direction) { case SOUTH : y++; break; case EAST : x++; break; case NORTH : y--; break; case WEST : x--; break; } // test for outside border if (x >= myWorld.getWidth() || y >= myWorld.getHeight()) { return false; } else if (x < 0 || y < 0) { return false; } return true; } /** * Turns towards the left. */ public void turnLeft() { switch(direction) { case SOUTH : setDirection(EAST); break; case EAST : setDirection(NORTH); break; case NORTH : setDirection(WEST); break; case WEST : setDirection(SOUTH); break; } } /** * Sets the direction we're facing. */ public void setDirection(int direction) { this.direction = direction; switch(direction) { case SOUTH : setRotation(90); break; case EAST : setRotation(0); break; case NORTH : setRotation(270); break; case WEST : setRotation(180); break; default : break; } } /** * Tell how many leaves we have eaten. */ public int getLeavesEaten() { return leavesEaten; } }

Some Useful Methods that Wombats can use

Method	Meaning
getRotation()
setRotation( 5)	sets Wombat’s rotation to 5
setRotation(getRotation() + 5)	gets the Wombat’s current rotation + 5 setDirection(WEST);
canMove()	returns a boolean that lets you know whether or not there is anything blocking the path of a Wombat, like the edge of the world etc..
move()	this a long method that does many things. Mainly though, if(canMove() == true) the wombat moves forward, otherwise it turns left
turnLeft()	pretty self descriptive!

Part III Assignments for my students

• Task #1) Modify the Wombat class so that it takes 30 steps and stops.
• Task #2) Modify the Wombat class so that every 4 steps that it makes it will turn left. Note: The wombat will still have to turn left if it hits a wall before taking 5 steps. Whenever the Wombat hits a wall, reset the number of steps to zero. Hint: Most of your modifications to this class should go in the act() method.
• Task #3) Modify the WOmbat class so that it only eats every other leaf that it finds.
• Task #4) Look at the TurnLeft() method, the code is reproduced below.. Make a similar method but that is called TurnRight()

  
      public void turnLeft()
      {
          switch(direction) {
              case SOUTH :
                  setDirection(EAST);
                  break;
              case EAST :
                  setDirection(NORTH);
                  break;
              case NORTH :
                  setDirection(WEST);
                  break;
              case WEST :
                  setDirection(SOUTH);
                  break;
          }
      }
  
  
    

• Task#5) Create a wombat that makes 2 steps and tries to turn in a random direction (up,down,left or right).
  • Her's how to create random numbers in java

  How to Change a double to an int
  double myDouble = 1.4;
  int myInt = (int) myDouble; // (int) 'casts' the data to an int
  
  How to Create a Random int
  double randD = Math.random(); //between 0 and .99999999
  //flipACoin  is always either 1 or 2
  //because .999 * 2 = 1.99800 which becomes 1 if we're dealing with an int
  int flipACoin =  (int)(randD *2); //multiply by 2, truncate
  int oneThroughThree= (int) (randD *2  + 1); 
  

  Move on to the next lesson and Labs