user interface - Java - Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException error -

i creating simple game in java. here code. gui class:

public class gui extends jframe implements actionlistener{  jbutton upbutton, downbutton, leftbutton, rightbutton;  game game; player player; board b; maze maze; player pl;  public gui () {     b= new board();     game game = new game(b);       setsize(800,600);     container cp = getcontentpane();      upbutton = new jbutton("up");     downbutton = new jbutton("down");        leftbutton = new jbutton("left");     rightbutton= new jbutton("right");     upbutton.addactionlistener(this);     downbutton.addactionlistener(this);     leftbutton.addactionlistener(this);     rightbutton.addactionlistener(this);      jpanel p = new jpanel();     boxlayout boxlayout1 = new boxlayout(p, boxlayout.y_axis);     p.setborder(borderfactory.createemptyborder(250, 0, 250, 0));     p.setlayout(boxlayout1);      jpanel panel_1 = new jpanel();     p.add(panel_1, borderlayout.north);      jpanel panel_2 = new jpanel();     p.add(panel_2);      jpanel panel_3 = new jpanel();     p.add(panel_3, borderlayout.after_last_line);      panel_1.add(upbutton);     panel_2.add(leftbutton);     panel_2.add(rightbutton);     panel_3.add(downbutton);      cp.setlayout(new borderlayout());     cp.add(p, borderlayout.east);      game= new game(b);     cp.add(game, borderlayout.center); }   public void actionperformed(actionevent e) {     if(upbutton == e.getsource()){         game.moveplayerup();         system.out.println("up");         }     if(downbutton == e.getsource()){         game.moveplayerdown();         system.out.println("down");         repaint();         }     if(leftbutton == e.getsource()){         game.moveplayerleft();         repaint();         system.out.println("left");         }     if(rightbutton == e.getsource()){         game.moveplayerright();         repaint();         system.out.println("right");         }     game.repaint();     } public static void main(string[] args) {     gui frame = new gui();     frame.setvisible(true); } 

}

this game class:

public class game extends canvas {

int m; int n;  // margin board b; double tokensize, markingsize; int[][] marking; int pickuptype; int pickupx, pickupy; dimension lastsize; image picture; maze maze; player player;  boolean ingame = false;  boolean dying = false;  boolean finished = false; thread gamethread = null;  int pposition [][]; public int positiona; public int positionb;  public final font smallfont = new font("helvetica", font.bold, 14);  public game (board db) {     pposition = new int[4][4];     maze = new maze();     b=db;     m=20;     setbackground(color.lightgray);     lastsize=getsize();     picture=createimage(lastsize.width, lastsize.height);     createplayerboard();     setinitialplayerposition(); }  public void paint (graphics g){     update(g); }  public synchronized void update(graphics g1) {      dimension d=getsize();     if (!d.equals(lastsize)) {         picture=createimage(d.width, d.height);     }       graphics g=picture.getgraphics();      g.setcolor(getbackground());     g.fillrect(0, 0, d.width, d.height);     g.setcolor(getforeground());     g.drawrect(0, 0, d.width-1, d.height-1);     int h=getheight();     int w=getwidth();      int squaresize = math.max(0,(math.min(h,w)-2*m))/8;     squaresize = squaresize+40;      graphics2d g2 = (graphics2d) g;     image img1 = toolkit.getdefaulttoolkit().getimage("3down.jpg");     image img2 = toolkit.getdefaulttoolkit().getimage("3left.jpg");     image img3 = toolkit.getdefaulttoolkit().getimage("3right.jpg");     image img4 = toolkit.getdefaulttoolkit().getimage("3up.jpg");     image img5 = toolkit.getdefaulttoolkit().getimage("all4.jpg");     image img6 = toolkit.getdefaulttoolkit().getimage("down_left.jpg");     image img7 = toolkit.getdefaulttoolkit().getimage("down_right.jpg");     image img8 = toolkit.getdefaulttoolkit().getimage("up_left.jpg");     image img9 = toolkit.getdefaulttoolkit().getimage("up_right.jpg");     image img10 = toolkit.getdefaulttoolkit().getimage("cyclops.gif");      //this code displays board      (int i=0; i<5; i++) {         (int j=0; j<5; j++) {             if(i==0&&j==0){             g2.drawimage(img7,m + * squaresize, m + j * squaresize, squaresize, squaresize, this);             g2.finalize();}             else if(i==1&&j==0){             g2.drawimage(img1,m + * squaresize, m + j * squaresize, squaresize, squaresize, this);             g2.finalize();}             else if (i==2&&j==0){             g2.drawimage(img1,m + * squaresize, m + j * squaresize, squaresize, squaresize, this);             g2.finalize();}             else if (i==3&&j==0){             g2.drawimage(img1,m + * squaresize, m + j * squaresize, squaresize, squaresize, this);             g2.finalize();}             else if (i==4 &&j==0){             g2.drawimage(img6,m + * squaresize, m + j * squaresize, squaresize, squaresize, this);             g2.finalize();}     }      //this code display cyclop      loadplayerposition();     int x=positiona;     int y=positionb;      g2.drawimage(img10,m + x * squaresize, m + y * squaresize, squaresize, squaresize, this);     g2.finalize();  g1.drawimage(picture,0,0,null); }     //this method creates player board , fills places in array 0 public void createplayerboard(){     (int = 0; < pposition.length; i++){         (int j = 0; j < pposition.length; j++){                 pposition[i][j] = 0;         }     } }  //this method sets initial player position in array public void setinitialplayerposition(){     pposition[0][0] = 1;  }  //this method changes interger positiona , positib be, integers represent current player position public void loadplayerposition(){     (int = 0; < pposition.length; i++){         (int j = 0; j < pposition.length; j++){             if(pposition [i][j] == 1){                 positiona=i;                 positionb=j;                     }         }     } }  //these methods change number in player array 0 1, deppending on button player clicked  public void moveplayerup(){     (int = 0; < pposition.length; i++){         (int j = 0; j < pposition.length; j++){             if(pposition [i][j] == 1){                 pposition [i][j] = 0;                 pposition [i][j+1] = 1;                     }         }     } }  public void moveplayerdown(){     (int = 0; < pposition.length; i++){         (int j = 0; j < pposition.length; j++){             if(pposition [i][j] == 1){                 pposition [i][j] = 0;                 pposition [i][j-1] = 1;                     }         }     } }  public void moveplayerleft(){     (int = 0; < pposition.length; i++){         (int j = 0; j < pposition.length; j++){             if(pposition [i][j] == 1){                 pposition [i][j] = 0;                 pposition [i-1][j] = 1;                     }         }     } }  public void moveplayerright(){     (int = 0; < pposition.length; i++){         (int j = 0; j < pposition.length; j++){             if(pposition [i][j] == 1){                 pposition [i][j] = 0;                 pposition [i+1][j] = 1;                     }         }     } } 

}
board class:

public class board {

int[][] b; maze maze; boolean alive = true; public int playerscore = 0; maze m;    public board() {      } 

}

the program creates windows buttons, displays board , displays player icon. want is: when player clicks on right button, icon moves right on array. when click on button, error:

exception in thread "awt-eventqueue-0" java.lang.nullpointerexception

i try search error , says happens when program points object null.however, think object not null. can give me advice please? thank much