[Simple_Condolences]

Quote

Alright, so, everything compiles just fine and even puts everything in the grid when I run it. However, before the first step in the program executes, I receive a nullPointerException. Any help squashing this bug would be greatly appreciated.

EDIT: Yes, this is all from the Gridworld API. I -hate- Gridworld.

Quote

A Ghost extends Critter.
When it acts, there is a 20% chance it will move towards a PacMan Critter and a 80% chance it will move randomly in ANY direction (which, by the definition of randomness, may include moving towards a PacMan Critter).
Ghosts eat PacMan critters but nothing else.
When a Ghost moves from a location A to a location B, location A should have a pill if it had one before the ghost, or not have a pill if it didn’t have one before the ghost. (Think about using class level Booleans to accomplish this.)
(If your Ghost Critter doesn’t work correctly, your project score will not be higher than an 80.)

import info.gridworld.actor.Actor;
import info.gridworld.actor.Critter;
import info.gridworld.grid.Grid;
import info.gridworld.grid.Location;
import java.awt.Color;
import java.util.ArrayList;

/**
 *
 * @author Zach
 */

public class Ghost extends Critter {
    Grid<Actor> gr = getGrid();
    private boolean lastMove = true;
    private boolean thisMove = true;

    public Ghost(Color col) {
        setColor(col);
    }

    @Override
    public void act() {
        if(getGrid() == null)
            return;
        ArrayList<Actor> actors = getActors();
        processActors(actors);
        ArrayList<Location> moveLocs = getMoveLocations();
        Location loc = selectMoveLocation(moveLocs);
        makeMove(loc);
    }

    @Override
    public void processActors(ArrayList<Actor> actors) {
        eatPacMan();
        
    }

    public void eatPacMan() {
        Location loc = getLocation();
        Location loc2;
        Actor a;

        for(int dir = 0;dir<360;dir+=15) {
            loc2 = loc.getAdjacentLocation(dir);
            if(gr.isValid(loc2)) {
                a = gr.get(loc2);
                if(a instanceof PacMan)
                    a.removeSelfFromGrid();
            }
        }
    }

    public ArrayList<Location> getMoveLocation() {
        ArrayList<Location> locs = gr.getValidAdjacentLocations(getLocation());
        for(int i = locs.size()-1; i>0 ;i++) {
            if(!(gr.get(locs.get(i)) instanceof PacMan) &&
               !(gr.get(locs.get(i)) instanceof Pill))
                locs.remove(i);
        }
        return locs;
    }

    @Override
    public Location selectMoveLocation(ArrayList<Location> locs) {
        int n = locs.size();
        Location loc = getLocation();
        double r = Math.random();
        if(r  <= 0.2)
           return loc.getAdjacentLocation(loc.getDirectionToward(findPacMan()));
        else
            return locs.get((int)(Math.random() * n));
    }

    @Override
    public void makeMove(Location loc) {
        Location loc2 = getLocation();
        if(loc == null)
            removeSelfFromGrid();
        else {
            if(gr.get(loc) instanceof Pill)
                thisMove = true;
            else
                thisMove = false;

            moveTo(loc);

            if(lastMove == true)
                gr.put(loc2, new Pill());
        }
        lastMove = thisMove;
    }

    public Location findPacMan() {
        Location loc = new Location(0, 0);
        ArrayList<Actor> actors = getActors();
        for(Actor a: actors) {
            if(a instanceof PacMan)
                loc = a.getLocation();
        }
        return loc;
    }
}

Error thrown:

Quote

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at Ghost.eatPacMan(Ghost.java:47)
at Ghost.processActors(Ghost.java:36)
at Ghost.act(Ghost.java:28)
at info.gridworld.actor.ActorWorld.step(ActorWorld.java:68)
at info.gridworld.gui.GUIController.step(GUIController.java:134)
at info.gridworld.gui.GUIController$4.actionPerformed(GUIController.java:247)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
at java.awt.Component.processMouseEvent(Component.java:6263)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3267)
at java.awt.Component.processEvent(Component.java:6028)
at java.awt.Container.processEvent(Container.java:2041)
at java.awt.Component.dispatchEventImpl(Component.java:4630)
at java.awt.Container.dispatchEventImpl(Container.java:2099)
at java.awt.Component.dispatchEvent(Component.java:4460)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4574)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4238)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4168)
at java.awt.Container.dispatchEventImpl(Container.java:2085)
at java.awt.window.dispatchEventImpl(window.java:2475)
at java.awt.Component.dispatchEvent(Component.java:4460)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)

Thrown at:

public void eatPacMan() {
        Location loc = getLocation();
        Location loc2;
        Actor a;

        for(int dir = 0;dir<360;dir+=15) {
            loc2 = loc.getAdjacentLocation(dir);
            if(gr.isValid(loc2)) { //line 47
                a = gr.get(loc2);
                if(a instanceof PacMan)
                    a.removeSelfFromGrid();
            }
        }
    }

Requested code:

public boolean isValid(Location loc) {
    return 0 <= loc.getCol() && loc.getRow() < getNumRows()
            && 0 <= loc.getCol() && loc.getCol() < getNumCols();
}

//I am not given the source code for the below method

public Location getAdjacentLocation(int direction)
        returns the adjacent location in the direction that is closest to direction

Quote

-E get(Location loc) returns an object at the Location loc
-E getAdjacentLocation(Direction dir) returns a location in direction dir from object E
-E getLocation() returns the location of object E
- getActors() returns an ArrayList<Actor> of all actors on the grid
- getGrid() returns the grid of type Actor which all of the objects lie in

I can provide the source code for all of these methods and any others in this program if needed. Thanks for taking a look.

- Zach

This post has been edited by Simple_Condolences: 22 March 2010 - 07:08 PM

[macosxnerd101]

I notice fairly often that you do not validate the adjacent Location. It is most likely one of these that is causing your NullPointerExceptions. If you could post the error message and the code at that line, we might be able to help you more.

Actor a = gr.get(loc.getAdjacentLocation(getDirection())); 

[Simple_Condolences]

Main post updated. Current code and error messages are posted.

Thanks for everything.

- Zach

[macosxnerd101]

Somehow, it seems that loc2 is null when you invoke the getAdjacentLocation() method. You may want to try testing it for a null reference before invoking the Grid isValid() method.

Quote

public boolean isValid(Location loc) { 
    return 0 <= loc.getCol() && loc.getRow() < getNumRows() 
            && 0 <= loc.getCol() && loc.getCol() < getNumCols(); 
} 
 
//I am not given the source code for the below method 
 
public Location getAdjacentLocation(int direction) 
        returns the adjacent location in the direction that is closest to direction

What are you talking about not given the source code? Both methods are part of the GridWorld framework. The isValid() method is part of the Grid<E> interface, and getAdjacentLocation() is part of the Location class.

[macosxnerd101]

Don't worry, I'm in AP CS too this year, so I have my own copy of GridWorld. It just sounded from what you were saying that you didn't have access to the source code for the GridWorld classes; which if you have the framework, isn't shouldn't be the case.

[Dogstopper]

I.HATE.GRIDWORLD.

[macosxnerd101]

Me too. At least the FRQ isn't graded by a compiler, and the Multiple Choice questions are a little more straight forward. We just finished with GridWorld today in AP CS (which marks the end of any new material for the AP exam), and are starting to review. Hopefully next marking period we'll go onto some AB level topics.

[macosxnerd101]

We are issued laptops for the school year by the county, so that's why we're so far ahead. And yes- recursion is on the AP Exam, and it's fairly big on the multiple choice.

[Dogstopper]

Simple_Condolences, on 23 March 2010 - 11:15 PM, said:

Dogstopper, on 23 March 2010 - 07:10 AM, said:

I.HATE.GRIDWORLD.

Can I quote you in my signature? lolol. I despise gridworld. Logic that isn't flawed has flaws... it makes NO sense... God I can't wait to be done... we have our test on it tomorrow and then we move on to recursion I think... kinda sucks we don't cover exception handling... Oh well! We've got tutorials for a reason!

- Zach

Yes! Feel free!

Simple_Condolences, on 23 March 2010 - 11:25 PM, said:

macosxnerd101, on 23 March 2010 - 07:52 AM, said:

Me too. At least the FRQ isn't graded by a compiler, and the Multiple Choice questions are a little more straight forward. We just finished with GridWorld today in AP CS (which marks the end of any new material for the AP exam), and are starting to review. Hopefully next marking period we'll go onto some AB level topics.

Where do you go to school? And I wonder if our AP exam has recursion on it... haha I dunno. I'll find out tomorrow morning.

- Zach

Yes, national exam so it will have recursion in it. Perhaps in the free-write section, you my have to write one.

[macosxnerd101]

Recursion is usually a multiple choice topic, not free-response. It's tested more in a manner of "given this method and inputs, what is the output" type question.