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)

read around on how to run from command line and copy error msgs. Is it an applet? if so run using appletviewer and in browser learn to enable Java console so can see error messages there — tgkprog, Jan 05 '14 at 08:18
The framework is responsible for providing the graphics context, you will need to ascertain how painting is achieved using the API before embarking much further.... — MadProgrammer, Jan 05 '14 at 08:31

score 1 · Accepted Answer · answered Jan 05 '14 at 10:59

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");
}

answered Jan 05 '14 at 10:59

Njol

3,271
17
32

Thank you very much, it worked! Well, I have learned even more now :P. This site should seriously pay you Njol. – MrPork Jan 05 '14 at 17:09

Calling a method with Graphics g as perimeter

1 Answers1