Implementing methods from other classes

Question

I am not able to understand why is it not working?

I've got my methods class:

package particles;

import org.newdawn.slick.Color;
import org.newdawn.slick.Graphics;

public class Methods {
Graphics g;

public void showhud(){
    g.setColor(Color.white);
    g.drawString("Screen: Game", 675, 10);
    g.drawString("Version: 1.0", 675, 25);
    }

}

But when i try to implement showhud() in my other class, it doesn't work!

This is how im using it:

package particles;

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;
import particles.Methods;

public class Game extends BasicGameState {
Methods m;

public void init(GameContainer container, StateBasedGame game) throws SlickException {

}

public void render(GameContainer container, StateBasedGame game, Graphics g) throws SlickException {
    m.showhud();
}

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

}

public int getID() {
    return 0;
}

}

The error i get is:

Tue Jan 01 17:19:36 NZDT 2013 ERROR:null
java.lang.NullPointerException
at particles.Game.render(Game.java:18)
at org.newdawn.slick.state.StateBasedGame.render(StateBasedGame.java:207)
at org.newdawn.slick.GameContainer.updateAndRender(GameContainer.java:703)
at org.newdawn.slick.AppGameContainer.gameLoop(AppGameContainer.java:456)
at org.newdawn.slick.AppGameContainer.start(AppGameContainer.java:361)
at particles.Main.main(Main.java:23)

Answer 1

You haven't initialized m - it's (still) null , so when you execute

m.showhud();

you get a NPE because m is null .

You must assign an instance of Methods to the variable m

Answer 2

You never assign a reference to g . In other words, you don't have a g = ... anywhere in your code. As such, when your Methods class is instantiated, g is initialised to the default value, which is null .

Answer 3

you havent initialised the Methods m object

by your code, i believe int() method should have initialised the m object

Answer 4

You may need to instantiate both class members references, g and m . Currently, both references are pointing to nothing. They must point to Graphics and Methods objects respectively.

1. If possible, add a constructor to Methods class that will take care of initializing g .

2. If init() is the start of Game's (your class) lifecycle, then initialize m in this state/block.