I am getting a null pointer exception in the constructor of this class and I don't know why Slick2d Bullet

Question

I am writing a platformer and just programmed this class for a bullet. I am getting an NPE in the constructor and I can't see what is wrong, here is my code:

package com.ncom.src.entity;

import org.newdawn.slick.GameContainer;
import org.newdawn.slick.Graphics;
import org.newdawn.slick.Image;
import org.newdawn.slick.SlickException;
import org.newdawn.slick.geom.Vector2f;

import com.ncom.src.Camera;
import com.ncom.src.world.World;

public class Bullet extends HealthEntity {
public Vector2f velocity;
public double angle;
private int timeout = 0;

public Bullet(int lx, int ly, World w, float x, float y) {
    super(lx, ly, 5, 5, w, 0);
    double hyp =  Math.sqrt((x - 600) * (x - 600) + (y - 400) * (y - 400));
    angle = Math.asin(y - 400/ hyp);

    velocity.y = (float) Math.sin(angle) * 0.4f;
    velocity.x = (float) Math.cos(angle) * 0.4f;
}

@Override
public void render(Graphics g, Camera c) throws SlickException {
    g.drawImage(new Image("res/actors/bullet.png"), locationX + c.camModX, locationY + c.camModY);
}

@Override
public void update(GameContainer gc, int delta) throws SlickException {
    if (timeout > 400) {
        this.dead = true;
    }
    else {
        locationX += velocity.x;
        locationY += velocity.y;
        timeout += 0.4f;
    }
}
}

I am basically trying to calculate the x component and the y component of a vector to move the bullet by. The x and y in the constructor stand for where the mouse was clicked.

And where do you get that NPE? Basically, the only possibility I see here is that `w` is null (or some method in it returns null) and that `super()` dislikes that; therefore it is in some code you do not show. — fge, Jun 16 '13 at 18:08
Please post the stacktrace and indicate which line causes the NPE. — Code-Apprentice, Jun 16 '13 at 18:08
Yes, it will be velocity since you never initialize it. Please always show us your stacktrace and indicate which line throws the NPE. We appreciate it *greatly* if you don't force us to guess. — Hovercraft Full Of Eels, Jun 16 '13 at 18:13

score 2 · Accepted Answer · answered Jun 16 '13 at 18:10

2

velocity is null, that is the obvious case. Or possibly your World w parameter could be null and cause an NPE in the superclass constructor. That's the only two things that can possibly be null in your Bullet constructor, as far as I can see.

answered Jun 16 '13 at 18:10

Harald K

26,314
7
65
111

Yes thank-you, I hadn't initialised the velocity! Face-palm – Dr_N Jun 16 '13 at 18:16

score 0 · Answer 2 · answered Jun 16 '13 at 18:22

0

If u can't use debugger, just put print statements after every line in your constructor or ever u think exception can be.

answered Jun 16 '13 at 18:22

Gudron

23
4

I am getting a null pointer exception in the constructor of this class and I don't know why Slick2d Bullet

2 Answers2