NullPointerException debugging help

Question

I need to know why I'm getting a NullPointerException during the buildSchedule method of my model; I'm building an agent-based model, and I have no idea why this is happening. I'm including the two classes that are giving me problems:
Here is Surfer.java:
public class Surfer implements Drawable {
     //class variables
     public static int                   surfer;
     public static int                   swimmer;
     public static int                   empty;
     public static int                          nextID = 0; // to give each an ID
     public static Object2DTorus          world;  // where the surfers live
     public Vector                       surferNeighbors;
     public Vector                       emptyNeighbors;
     public Vector                       vector;
     //instance variables
     int     ID;
     int x, y;
     // the Surfer constructor
     public Surfer ( ) {
          ID = nextID++;
          x = 0;
          y = 0;
          surferNeighbors = new Vector();
          emptyNeighbors = new Vector();
     public void step () {          
          int moved = 0; // Has not yet moved this step
          int totalSurferNeighbors = surferNeighbors.size();
          int totalEmptyNeighbors = emptyNeighbors.size();
          double happyRatio = (totalSurferNeighbors + totalEmptyNeighbors)/8.00;
          vector = world.getMooreNeighbors(x, y, false);
          for ( int i = 0; i < vector.size(); i++ ){
               Object o = vector.get(i);
               if (o instanceof Surfer)
                         surferNeighbors.add(o);
               System.out.printf("==> surfers getting added to list now");
               //     if ( vector.elementAt( i ) == null )
                    //          Surfer aSurfer = new Surfer();
               //          emptyNeighbors.add( aSurfer );//FIX ME LATER
          //Is the Surfer happy? ( >= 33% similarity)
          //Empty and similar count as happy; dissimilar counts as unhappy;
          if ( happyRatio > 0.34  == true ) {//The Surfer is happy; they end their move
               System.out.printf("    -- is happy right here!");
          // Otherwise, the Surfer is unhappy; they seek to move
          int maxTries = 50;  // P tries only 50 times to place itself
          int tries = 0;  // P begins its count at zero
          int newX, newY;  //
          //  P now begins to move square by square to find a spot
          do {
               newX = x + Random.uniform.nextIntFromTo( -1, 1 );
              newY = y + Random.uniform.nextIntFromTo( -1, 1 );
               ++tries;  //  P tries again and again to find a spot
          } while (  world.getObjectAt( newX, newY ) != null && tries <= maxTries );
          // P tries to move from where she was to where she wants to be
          if (  world.getObjectAt( newX, newY ) == null ) {  // Square is empty!
               world.putObjectAt( x, y, null );          // Make that cell empty
               world.putObjectAt( newX, newY, this );  // P moves to new home
               x = SimUtilities.norm( newX, world.getSizeX() ); // normalize for
               y = SimUtilities.norm( newY, world.getSizeY() ); //    torus
               System.out.printf( "    -- moved to new x,y=%d,%d.\n", x, y );
          else {
               System.out.printf( "    -- couldn't find a place to move! tries=%d\n",
                                      tries);
     // setters and getters
     public void setID(int i) {     
          ID = i;
     public int getID() {
          return ID;
     // This class method sets the class variables
     public static void setWorld( Object2DTorus world ) {
          world = world;
     public int getX() { return x; }
     public void setX( int i ) { x = i; }
     public int getY() { return y; }
     public void setY( int i ) { y = i; }
     // The Surfer needs to be able to draw itself.  As a result,
     // I use the Drawable method to let the Surfers make themselves
     // visible on the GUI.  That bit is found at the very top.
    public void draw( SimGraphics g ) {
          g.drawFastRoundRect( Color.green );
}And the overarching Model.java:
public class Model extends SimModelImpl {
     //instance variables
     private int                     numSurfers = 0;
     private int                     numSwimmers =0;
     private ArrayList                   surferList = new ArrayList ();
     private ArrayList               swimmerList = new ArrayList ();
     private ArrayList               allList = new ArrayList ();
         private Schedule               schedule;
         private int                      sizeX = 8, sizeY = 8; // integer size of the world
          private Object2DTorus         world;                    // RePast version of Torus
         private Object2DDisplay       worldDisplay;           // Makes the display 2D
         private DisplaySurface           dsurf;                     // Displays the surface
     public static void main(String[] args) { // Here's where the Model starts.
         System.out.printf( "==> enter main..." );
          uchicago.src.sim.engine.SimInit init = new uchicago.src.sim.engine.SimInit ();
          Model model = new Model ();
          // Is there any portion of the model that is incomplete?
          if (args.length > 0)
               init.loadModel (model, args[0], false);
          else
               init.loadModel (model, null, false);
          System.out.printf( "<== main done." );
    // constructor
     public Model () {
          System.out.printf( "==> Model constructor...\n" );
     public void setup () {
          System.out.printf( "==> setup...\n" );
          schedule = null;
          System.gc ();
          // default System.out and .err to terminal window especially for Windows.
          // Used when on a Windows machine to send output to a separate text file.
          // If on a Windows machine, uncomment and set to "true".
          //AbstractGUIController.CONSOLE_ERR = false; 
          //AbstractGUIController.CONSOLE_OUT = false;
          schedule = new Schedule (1);
          numSwimmers = 20;
          numSurfers = 20;
          swimmerList = new ArrayList ();
          surferList = new ArrayList ();
          sizeX = 8;  sizeY = 8;  // Traditional world size.
          // set up the display surface, linking it to this (Model)
          if ( dsurf != null )
                dsurf.dispose();
          dsurf = new DisplaySurface( this, "Player Display" );
          registerDisplaySurface( "Main Display", dsurf );
          System.out.printf( "<== setup done.\n" );
     public void begin () {
          System.out.printf( "==> begin...\n" );
          buildModel ();
          buildDisplay ();
          buildSchedule ();
          System.out.printf( "==> begin about to display dsurf...\n" );
          dsurf.display();
          System.out.printf( "<== begin done.\n" );
     private void buildModel () {
          System.out.printf( "==> buildModel...\n" );
          // create a uniform random variate generator.
        Random.createUniform();
          // create the 2D world, tell the Surfer and Swimmer classes about it.
          world = new Object2DTorus( sizeX, sizeY );
          Surfer.setWorld( world );
          Swimmer.setWorld( world );
          // create Swimmers and Surfers, place them at random in the 2D world.
          // note only one Agent per cell!
          Surfer aSurfer;
          Swimmer aSwimmer;
          int randomX, randomY;
          for ( int i = 0; i < numSurfers; i++ ) {
               aSurfer = new Surfer();
               surferList.add( aSurfer );
               allList.add( aSurfer );
               // Tells Surfers to find new places
               do {
                    randomX =  Random.uniform.nextIntFromTo( 0, world.getSizeX () - 1 );
                   randomY =  Random.uniform.nextIntFromTo( 0, world.getSizeY () - 1 );
               } while ( world.getObjectAt( randomX, randomY ) != null );
               world.putObjectAt( randomX, randomY, aSurfer );
               aSurfer.setX( randomX );
               aSurfer.setY( randomY );
               int asurferID = aSurfer.getID();
               System.out.printf( "    - created surfer with ID=%d placed at x,y=%d,%d.\n",
                                      asurferID, aSurfer.getX(), aSurfer.getY() );
          for ( int i = 0; i < numSwimmers; i++ ) {
               aSwimmer = new Swimmer();
               swimmerList.add( aSwimmer );
               allList.add( aSwimmer );
               // Tells Swimmers to find new places
               do {
                    randomX =  Random.uniform.nextIntFromTo( 0, world.getSizeX () - 1 );
                   randomY =  Random.uniform.nextIntFromTo( 0, world.getSizeY () - 1 );
               } while ( world.getObjectAt( randomX, randomY ) != null );
               world.putObjectAt( randomX, randomY, aSwimmer );
               aSwimmer.setX( randomX );
               aSwimmer.setY( randomY );
               int aswimmerID = aSwimmer.getID();
               System.out.printf( "    - created swimmer with ID=%d placed at x,y=%d,%d.\n",
                                      aswimmerID, aSwimmer.getX(), aSwimmer.getY() );
          System.out.printf( "<== buildModel done.\n" );
     private void buildDisplay () {
          System.out.printf( "==> buildDisplay...\n" );
          // create the link between the dsurf and the Object2DTorus,
          // and tell parts about each other as needed. Hah!
          worldDisplay = new Object2DDisplay( world );
        worldDisplay.setObjectList( allList );
        dsurf.addDisplayableProbeable( worldDisplay, "Surfers");
          dsurf.addDisplayableProbeable( worldDisplay, "Swimmers");
        addSimEventListener( dsurf );
          System.out.printf( "<== buildDisplay done.\n" );
     private void buildSchedule () {
          System.out.printf( "==> buildSchedule...\n" );
          schedule.scheduleActionBeginning (1, this, "step");
     public void step () {
          System.out.printf( "==> Model step %.0f:\n", getTickCount() );// Checking step #
          for ( int i = 0; i < surferList.size(); i++ ) {
               Surfer aSurfer; // Makes new surfers when needed
               aSurfer = (Surfer) surferList.get (i);  // Identifies surfers
               aSurfer.step ();
          for ( int i = 0; i < swimmerList.size(); i++ ) {
               Swimmer aSwimmer; // Makes new swimmers when needed
               aSwimmer = (Swimmer) swimmerList.get (i);  // Identifies swimmers
               aSwimmer.step ();
          dsurf.updateDisplay();  // Updates the display with new surfers and swimmers and identities
          System.out.printf( "<== Model step done.\n" );
     // Another version of step(), which uses a common idiom
     // Note the definition of aBug is *inside* the for-loop,
     // and it gets its value on the same line.
     //public void stepX () {
     //     System.out.printf( "==> step %.0f:\n", getTickCount() );
     //     for ( int i = 0; i < bugList.size(); i++ ) {
     //          Bug aBug = (Bug) bugList.get (i);
     //          aBug.step ();
     public String[] getInitParam () {  // Looks at init params; places correct
          String[] params = { "numSurfers" };  // number of Ps from init params.
          //String[] params = { "numSwimmers" };
          return params;
     public Schedule getSchedule () {     return schedule; }  // Sets the timing
     public String getName () { return "Model"; }  // Just for output.
     // setters and getters
     public int getNumSurfers () { return numSurfers; } // These talk to P class
     public int getNumSwimmers () { return numSwimmers; }
     public void setNumSurfers (int numSurfers) {
          this.numSurfers = numSurfers;}
     //     public void setNumSwimmers (int numSwimmers) {
     //     this.numSwimmmers = numSwimmers;}
}What the hell am I doing wrong?

Answer 1

private void buildSchedule () {
    System.out.printf( "==> buildSchedule...\n" );
    schedule.scheduleActionBeginning (1, this, "step");
}Here is the code for your buidSchedule method. Apparently, the schedule object hasn't been instantiated yet.