Greenfoot Lesson: Movement

Movement Tutorial II

If you want to move an object in Greenfoot when it is intitialized you cannot do so directly in the constructor. You must create a method called addedToWorld().

Erroneous Code (tries using constructor)	Proper Code
public Wombat() { setLocation(1,1); }	public void addedToWorld(World world) { setLocation(1,1); }

How to tell your location

Method	Meaning
int getY()	returns an int that is the column value or y-cordinate of a tile
int getX()	returns an int that is the row value or x-cordinate of a tile

How far to the edge of the world?

To be able to tell how far to the edge of a world you must

• First create a world object

  	World myWorld = getWorld(); 
  	

• Second) call getWidth() or getWidth (If you haven't programmed much in Java before, look carefuly at the syntax below.

  	World myWorld = getWorld();
   	int widthOfWorld =  myWorld.getWidth()
    int heightOfWorld = myWorld.getHeight() ; 
  	

getX() vs width of the world

The picture below illustrates the values that getX() stores. NOTE: the getWidth() method of the world is 8 but the last value of getX() on the grid is 7.

Te first thing to look at is location changes. Consider, for example, the following code:

public void act()
{
	int x = getX(); 
	int y = getY();
	//move 1 to right
	setLocation(x + 1, y);
} 

My Students: create a new subclass of Actor called person. Copy and paste all of the code below into the class. Run the code and try to learn from what's printed out.

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 Person 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 void addedToWorld(World world) { // here is the method that you can use to set the original location } public Person() { double randD = Math.random(); //between 0 and .99999999 int flipACoin = (int)(randD *2); //this multiplies the random decimal by two then cuts of the decimal setDirection(NORTH); leavesEaten = 0; } public void showVariables(){ System.out.println("getX() " + getX()); System.out.println("getY() " + getY()); //create a "World" variable //this allows us to get the width and height of the world World myWorld = getWorld(); System.out.println("myWorld.getWidth() :" + myWorld.getWidth()); System.out.println("myWorld.getHeight() :" + myWorld.getHeight()); } public void act() { showVariables(); 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; } int moveAmount =2; switch(direction) { case SOUTH : setLocation(getX(), getY() + moveAmount); break; case EAST : setLocation(getX() + moveAmount, getY()); break; case NORTH : setLocation(getX(), getY() - moveAmount); break; case WEST : setLocation(getX() - moveAmount, 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; } }

Labs

Lab #1 ) Create a new class called WombatSearcher()

• You should be able to put a WombatSearcher() down anywhere on the grid. The first thing that it will do is randomly dhoose one of the four corners
• travel to that corner
• then it will traverse every row and column until it has visited all the cells and eaten ALL of the leaves that are on the grid