Calling a method with Graphics g as perimeter

Question

i am using slick2D to create a simple java game. Unfortunately my java skills are simpler than simple. This game will be a memory game, since i thought it would be simple to make. One of the problems i have is that i have a NormalMode class, and a Square class. I created a Square object in my normal mode class to call methods from Square. So, i tried to call a method of it that had "graphics g" as a perimeter, and as a result i get a null pointer exception error (Or something else i'm unaware of).

Square Class: (The last method in this class is unfinished at the moment)

       package data.src;

import java.util.Random;

import org.newdawn.slick.Graphics;
import org.newdawn.slick.Image;
import org.newdawn.slick.SlickException;
import org.newdawn.slick.state.StateBasedGame;

public class Square {

    private StateBasedGame game;
    boolean correct;
    boolean clickable;
    boolean clicked;
    boolean started;
    int squares;
    int squareX;
    int squareY;
    public Image squareIncorrect;
    public Image squareCorrect;

    public Square() {

                }



    public boolean checkCorrect(){
        return correct;

    }
    public boolean checkClickable(){
        return clickable;
    }

    public boolean checkClicked(){
        return clicked;

    }


        public void squareStart(int x ,int y, Graphics g){

            if(correct == true){
                g.drawImage(squareCorrect, x, y);
            }
            else if(correct == false){
                g.drawImage(squareIncorrect, x, y);
            }
            g.drawString("Remember the blue squares!", x, y);
            try {
                wait(3000);
            } catch (InterruptedException e) {

                e.printStackTrace();
            }
            started = true;
            while(started == true){
                try {
                    squareCorrect = new Image("res/squareCorrect");
                } catch (SlickException e) {

                    e.printStackTrace();
                }

            }

        }

    public void createRandom(){

        Random rand = new Random();
        int sRand = rand.nextInt(1);

            if(sRand == 0){
                correct = false;
                clickable = true;
                clicked = false;

            }
            else if(sRand == 1){
                correct = true;
                clickable = true;
                clicked = false;
                squares++;

            }
    }


    public void youWin(int x, int y, Graphics g){
        if(squares == 0){
            g.drawString("You win!", x, y);
            game.enterState(0);
        }
    }
}

Normal Mode Class:

package data.src;

import org.newdawn.slick.GameContainer;
import org.newdawn.slick.Graphics;
import org.newdawn.slick.SlickException;
import org.newdawn.slick.state.BasicGameState;
import org.newdawn.slick.state.StateBasedGame;

public class NormalMode extends BasicGameState {

    private Square[][] square = new Square[4][4];

    public NormalMode() {


                }

    @Override
    public void init(GameContainer arg0, StateBasedGame Game)throws SlickException {
                    for(int i = 0; i < square.length; i++){
                        for(int j = 0; j < square.length; j++){
                            square[i][j] = new Square();
                            square[i][j].createRandom();
                        }
                    }

            }

    @Override
    public void render(GameContainer container, StateBasedGame game, Graphics g)
            throws SlickException{
                square[1][1].squareStart(40, 300, g);

    }

    @Override
    public void update(GameContainer container, StateBasedGame game, int delta)
            throws SlickException {


    }

    @Override
    public int getID() {
        return 3;
    }


}

P.S: Excuse my complete nonsense of stuff if my code seems stupid.

The error:

Sun Jan 05 01:17:25 MST 2014 ERROR:null
java.lang.NullPointerException
    at org.newdawn.slick.Graphics.drawImage(Graphics.java:1384)
    at org.newdawn.slick.Graphics.drawImage(Graphics.java:1433)
    at data.src.Square.squareStart(Square.java:46)
    at data.src.NormalMode.render(NormalMode.java:32)
    at org.newdawn.slick.state.StateBasedGame.render(StateBasedGame.java:199)
    at org.newdawn.slick.ScalableGame.render(ScalableGame.java:158)
    at org.newdawn.slick.GameContainer.updateAndRender(GameContainer.java:688)
    at org.newdawn.slick.AppGameContainer.gameLoop(AppGameContainer.java:411)
    at org.newdawn.slick.AppGameContainer.start(AppGameContainer.java:321)
    at data.src.Core.main(Core.java:30)
Sun Jan 05 01:17:25 MST 2014 ERROR:Game.render() failure - check the game code.
org.newdawn.slick.SlickException: Game.render() failure - check the game code.
    at org.newdawn.slick.GameContainer.updateAndRender(GameContainer.java:691)
    at org.newdawn.slick.AppGameContainer.gameLoop(AppGameContainer.java:411)
    at org.newdawn.slick.AppGameContainer.start(AppGameContainer.java:321)
    at data.src.Core.main(Core.java:30)

Answer 1

squareCorrect and squareIncorrect are null because you don't set the variables before using them.

You should load them just after declaring them:

public Image squareIncorrect;
public Image squareCorrect;
{
    squareIncorrect = new Image("res/squareCorrect");
    squareIncorrect = new Image("res/squareIncorrect");
}