Null pointer exception multi-classes

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Null pointer exception multi-classes

in Programming Questions • 11 months ago

Hello, i've got a problem with my game.
I get a Null Pointer Exception.

I want the code to be clean and easy to read so the main class shall only contain the setup and draw void and a key handler. The voids used by the main class are supposed to be in another class called " voids".

So far i have only written the code supposed to draw the map (tile based).

My Main class:

//Using Eclipse
//Main class, clean version
import processing.core.*;
import java.awt.event.*;
public class Game2 extends PApplet implements KeyListener{
//Instancing classes
Player you = new Player();
maps map = new maps();
voids allVoids = new voids(); //the class causing errors
int lvl=1; //just for the development
public static void main(String[] args) {
PApplet.main(new String[] { "Game2" });
}
public void setup(){
size(1024,640);
}
public void draw(){
background(255);
allVoids.drawBox(); //calling the void from class "voids",
//supposed to be changed to a void drawing the map(background)
}
// Keypress -- works as far as i know, simply edits posX&posY from the player class
// to move the caracter. Outblocked to cause no errors
/*
public void keyPressed(KeyEvent e){
int keyCode = e.getKeyCode();
if (keyCode == KeyEvent.VK_RIGHT){
if(map.main[lvl][you.posY+1][you.posX+2]>999 || map.main[lvl][you.posY+1][you.posX+2]<900) you.posX++;
}
if (keyCode == KeyEvent.VK_LEFT){
if(map.main[lvl][you.posY+1][you.posX]>999 || map.main[lvl][you.posY+1][you.posX]<900) you.posX--;
}
if (keyCode == KeyEvent.VK_UP){
if(map.main[lvl][you.posY][you.posX+1]>999 || map.main[lvl][you.posY][you.posX+1]<900)you.posY--;
}
if (keyCode == KeyEvent.VK_DOWN){
if(map.main[lvl][you.posY+2][you.posX+1]>999 || map.main[lvl][you.posY+2][you.posX+1]<900)you.posY++;
}
else{
e.consume();
}
}*/
}

The maps class:

public class maps {
// simply contains an int array where every position represents a field,
// local variables are there to make different numbers represented equally long (square-ish shape)
// simply: int main[lvl][x][y]
int bdr=1; //outer border, hit when person leaves the field, to save space
//
// later on some of the bdr tiles are going to be changed to numbervalues like 030404
// so if the player walks on this tile the map is going to change to "lvl" 03 and the player will stand on
// tile 04,04
//
int emp=901; //empty field
int wll=20; //wall for test
public int main[][][]={
//map 1
// in Eclipse the letters have the same width, therefor are all tiles represented by
//three letters to make the viewing easier for me
{
{bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr},
{bdr,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,bdr},
{bdr,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,bdr},
{bdr,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,bdr},
{bdr,emp,emp,emp,emp,wll,wll,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,bdr},
{bdr,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,bdr},
{bdr,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,bdr},
{bdr,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,bdr},
{bdr,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,bdr},
{bdr,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,bdr},
{bdr,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,bdr},
{bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr}
},
//map 2
{
{bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr},
{bdr,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,bdr},
{bdr,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,bdr},
{bdr,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,bdr},
{bdr,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,bdr},
{bdr,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,bdr},
{bdr,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,bdr},
{bdr,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,bdr},
{bdr,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,bdr},
{bdr,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,bdr},
{bdr,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,bdr},
{bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr}
},
//map 3
{
{bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr},
{bdr,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,bdr},
{bdr,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,bdr},
{bdr,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,bdr},
{bdr,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,bdr},
{bdr,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,bdr},
{bdr,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,bdr},
{bdr,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,bdr},
{bdr,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,bdr},
{bdr,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,bdr},
{bdr,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,emp,bdr},
{bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr,bdr}
}
};
public maps(){} //constructor
}

And here the voids class causing problems:

import processing.core.*;
// class causing errors (i guess)
class voids extends PApplet{
//purpose, contain voids executed in the draw void to
//clean up the main class
public void drawBox(){ // void for testing
rect(5,5,50,50);
}
void drawMap(int map[][][], int lvl){
// Most necessary void: Two for-loops to get a number from the
// maps.main array and convert it to a picture (represented by
// a rectangle for testing purposes).
int m[][][]=map;
for(int a=0;a<=15;a++){
for (int b=0;b<=9;b++){
if (m[lvl][b][a]==901){
//draw empty
rect((a-1)*64,(b-1)*64,64,64);
}
if (m[lvl][b][a]==20){
//draw a wall
}
}
}
}
}

So the draw void is supposed to execute voids like allVoids.drawMap(), allVoids.drawPlayer(), allVoids.drawInventory().
But the rect() void in "voids" causes an Null Pointer Exception:

Exception in thread "Animation Thread" java.lang.NullPointerException

at processing.core.PApplet.rect(PApplet.java:11045)

at voids.drawBox(voids.java:5)

at Game2.draw(Game2.java:19)

at processing.core.PApplet.handleDraw(PApplet.java:2128)

at processing.core.PGraphicsJava2D.requestDraw(PGraphicsJava2D.java:190)

at processing.core.PApplet.run(PApplet.java:2006)

at java.lang.Thread.run(Thread.java:680)

Eclipse gives no more information than this so there are no spelling errors etc.
I could move the voids into the main class witch makes the program run, but then the main class gets so full and i want it clean ^^

Help and Comments appreciated, sorry for gramatical errors

//Differenze :)

Replies(1)

quarks

Re: Null pointer exception multi-classes

11 months ago

By convention all class names have the first letter capitilised so void >> Voids and maps >> Maps everything else (almost) should start with a lowercase letter. Might seem a little thing but when looking at many lines of code it helps identify the classes used. In Eclipse use the Refactor-name to change the name of an identifier - do NOT use search and replace

I assume that the voids class extends PApplet so that it can access the PApplet methods such as rect - this is a very bad idea and the wrong way to do it. In your Eclipse project (game) there should be just one class that inherits from PApplet (unless you are using multiple windows). What should happen is that the class must have an attribute of type PApplet which is set in the constructor then this would be used to perform any drawing. e.g. app.rect(...

import processing.core.*;
// class causing errors (i guess)
class voids PApplet{
PApplet app;
// The constructor sets the attribute
public voids(PApplet the Applet){
app = theApplet;
}
//purpose, contain voids executed in the draw void to
//clean up the main class
public void drawBox(){ // void for testing
app.rect(5,5,50,50);
}
void drawMap(int map[][][], int lvl){
// Most necessary void: Two for-loops to get a number from the
// maps.main array and convert it to a picture (represented by
// a rectangle for testing purposes).
int m[][][]=map;
for(int a=0;a<=15;a++){
for (int b=0;b<=9;b++){
if (m[lvl][b][a]==901){
//draw empty
app.rect((a-1)*64,(b-1)*64,64,64);
}
if (m[lvl][b][a]==20){
//draw a wall
}
}
}
}
}

Once you have done this then the a voids object must be created inside the setup method so change line 11 of your Main class code to

voids allVoids; //the class causing errors

and change setup to

public void setup(){
size(1024,640); // must be first line in setup
allVoids = new voids(this); // must happen after size method called
}

HTH

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