I need to make a Wombat move towards the closest leaf and eat it until they are all gone.
Are there any good examples of this sort of greedy behavior I can look at?
wallace989 wrote ...
2015/4/27
Greedy Behavior
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The code you create for this would be an example of this sort of greedy behavior. Basically, what you stated was this:
If the world is not empty of leaves,
if can see leaf, eat leaf;
else, turn and move toward closest leaf;
The way I stated it should not be difficult to turn into code. The different parts of it ('can see', 'eat leaf', 'turn and move toward closest leaf') can be method calls ('canSeeLeaf', 'eatLeaf' and 'approachLeaf'), each which can be given its appropriate code (again, state what it should do, simply; convert into a basic statement and call methods on any parts that need further scrutiny).
I will give an example of how the first line is converted to code -- If the world is not empty of leaves:
if (leavesRemain())
{
// rest of phrasing coded here
}
private boolean leavesRemain()
{
return !getWorld().getObjects(Leaf.class).isEmpty(); // is world not empty of leaves
}import greenfoot.*; // (World, Actor, GreenfootImage, and Greenfoot)
import java.util.List;
import java.awt.Font;
/**
* A Wombat.
*/
public class GreedyWombat 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 moves;
public GreedyWombat()
{
setDirection(EAST);
}
/**
* The Wombat executes its assigned behavior, increases the number of
* moves taken, and then checks if the last Leaf has been eaten.
*/
public void act()
{
wombatBehavior();
moves++;
checkComplete();
}
/**
* The Wombat behavior has to be implemented in this method.
* The Wombat should always take one step in the direction of the closest Leaf.
*/
public void wombatBehavior() {
if(foundLeaf()) {
eatLeaf();
}
else if(canMove()) {
move();
}
}
private boolean leavesRemain()
{
return !getWorld().getObjects(Leaf.class).isEmpty(); //is world not empty of leaves
}
/**
* The method to check if the last Leaf has been eaten by the Wombat.
* If the last Leaf has been eaten, the game stops and the number of moves
* taken by the Wombat is shown on the screen.
*/
public void checkComplete() {
List<Leaf> leaves = getWorld().getObjects(Leaf.class);
if(leaves.isEmpty()) {
getWorld().getBackground().setFont(new Font("Arial", 0, 30));
getWorld().getBackground().drawString("Number of moves: " + moves, 100, 175);
Greenfoot.stop();
}
}
/**
* 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) {
getWorld().removeObject(leaf);
}
}
/**
* Move one cell forward in the current direction.
*/
public void move()
{
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;
}
/**
* Changes the direction the Wombat is facing.
* This is relevant for the image shown and for the change in location
* executed by the move() method.
*/
public void setDirection(int direction)
{
this.direction = direction;
switch(direction) {
case SOUTH :
setImage("wombat.gif");
setRotation(90);
break;
case EAST :
setImage("wombat.gif");
setRotation(0);
break;
case NORTH :
setImage("wombat-left.gif");
setRotation(90);
break;
case WEST :
setImage("wombat-left.gif");
setRotation(0);
break;
default :
break;
}
getImage().scale(29,24);
}
}here is what I have to work with, so far the wombat just moves to the edge and stops
I do not see anywhere that you call 'setDirection' in another method outside the constructor (which you may want to do if you are not eating AND you cannot move).
The goal is to get the Wombat to eat the nearest leaf then move on to the next leaf until they are all gone.
By moving toward the nearest leaf the Wombats direction shouldn't have to be set?
/**
* The Wombat behavior has to be implemented in this method.
* The Wombat should always take one step in the direction of the closest Leaf.
*/
public void wombatBehavior() {
if(foundLeaf()) {
eatLeaf();
}
else if(canMove()) {
move();
//turn and move toward closest leaf?
}
}If you are to have the wombat behave as you intend, you will have to expand on the 'else' part of the 'wombatBehavior' method (lines 10 though 13). You will not be saying "if can move, then move". Presuming that there are no obstacles to avoid (rocks, walls, or trees, for examples), then once you find the closest leaf, the 'canMove' method will not need to be called because no edge should be present between the wombat and the leaf (or one would be already outside the world bounds). So, it is just a matter of finding the closest leaf, turning toward it (so that moving will decrease the difference between the x or y coordinates of the leaf and the wombat) and moving.
/**
* The Wombat behavior has to be implemented in this method.
* The Wombat should always take one step in the direction of the closest Leaf.
*/
public void wombatBehavior() {
if(foundLeaf()) {
eatLeaf();
}
else if(getObjectsInRange(2, "Leaf.class")) {
//turn towards nearest leaf and move in that direction
}
}Is this the correct way to start this? I am getting confused
wallace989 wrote...
Is this the correct way to start this? public void wombatBehavior() {
if(foundLeaf()) {
eatLeaf();
}
while(getNeighbours(2, 2, Leaf.class)) {
//turn towards nearest leaf and move in that direction
}
}Getting an error here how do you use this method?
public void wombatBehavior() {
if(foundLeaf()) {
eatLeaf();
}
while(getNeighbours(1, false, "Leaf.class")) {
//turn towards nearest leaf and move in that direction
}
}Also tried this still dosent work
For one thing, you are saying:
where you need:
For another thing, the '1' needs to be in a variable so you can increase it inside the 'while' code block.
if (<List>)
if (<Boolean>) // or if (<list is not empty>)
public void wombatBehavior() {
if(foundLeaf()) {
eatLeaf();
}
while(getNeighbours((1,false),(1,true) "Leaf.class")) {
//turn towards nearest leaf and move in that direction
}
}Something Like this? Or am I still missing the point entirely?
You are still missing the point, it seems. Now you use the method with even more complicated parameters which isn't possible. The parameters are 'int, int, class', so you have to use them. It returns a list, a list can't be an if condition, so you can check if the list isn't empty (which means that there is a leaf around you):
while(!getNeighbours(2, 2, Leaf.class).isEmpty())
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