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Index › Programming Questions & Help › Syntax Questions › Java question: Custom classes in Arrays

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Java question: Custom classes in Arrays (Read 1294 times)

Augusto

Java question: Custom classes in Arrays
Mar 25^th, 2010, 3:19am

I've created a simple class called Utility:

Code:

class Utility extends Tag {  
  String utilType;
  
  Utility(PImage ps, String type, float px, float py) {
    super(ps, px, py);
    utilType = type;
  }

  void draw() {
    imageMode(CENTER);
    
    image(icon, posX, posY);
  } 
}

Code:

class Tag {
  PImage icon;
  float posX, posY;
  
  Tag(PImage ic, float px, float py) {
    icon = ic;
    posX = px;
    posY = py;
  }
  
  void draw() {
    imageMode(CENTER);
    
    image(icon, posX, posY);
  }
}

If I try to draw an utility, like:

Code:

Utility taxiTest;
(...)
taxiImage = loadImage("taxi.png");
taxiTest = new Utility(taxiImage, "taxi", 298.25, 891.5);
(...)
taxiTest.draw();

Everything works great, but if I try to have an Array of utilities, like:

Code:

Utility[] taxis = new Utility[6];
(...)
for (int i = 0; i < 6; i++) {
    (...)
    taxis[i] = new Utility(taxiImage, "taxi", p.x, p.y);
}
(...)
taxis[5].draw();

Causes an NullPointerException inside the Utility's draw() method on:

Code:

image(icon, posX, posY);

I tried printing taxi[5].posX, and it works.

Any clues on why I'm having this error?

« Last Edit: Mar 25^th, 2010, 5:06am by Augusto »

Augusto Junior Member Offline Posts: 55 Portugal	Re: Java question: Custom classes in Arrays Reply #1 - Mar 25^th, 2010, 4:00am Tried also with an ArrayList but I'm having the same error, now in: Code: taxis.add(new Utility(taxiImage, "taxi", p.x, p.y)); Is it because of the image? But why does this happen only when I try to add these objects to arrays?

PhiLho

Re: Java question: Custom classes in Arrays
Reply #2 - Mar 25^th, 2010, 4:47am

I don't know if it is related, but you have an extra closing brace before Tag's draw() method.
Beside, if the method is the same, you don't need to redefine Tag's draw() in Utility class.
Is taxiImage defined before your loop? Since you show only partial code without important part (context), it is hard to guess.

Augusto

Re: Java question: Custom classes in Arrays
Reply #3 - Mar 25^th, 2010, 5:05am

PhiLho wrote on Mar 25^th, 2010, 4:47am:

I don't know if it is related, but you have an extra closing brace before Tag's draw() method.
Beside, if the method is the same, you don't need to redefine Tag's draw() in Utility class.
Is taxiImage defined before your loop Since you show only partial code without important part (context), it is hard to guess.

The extra closing brace is because of a a bad copy/paste. I have in all examples:

Before setup():
Code:

PImage taxiImage

Inside setup():
Code:

taxiImage = loadImage("taxi.png");

I wonder why the image is causing this problem when it's put within an array (as part of an object) Undecided

yconst Junior Member Offline Posts: 75	Re: Java question: Custom classes in Arrays Reply #4 - Mar 25^th, 2010, 1:58pm The only thing that comes in mind is that since the image is passed by reference to the objects it is essentially the same right? So, if the original is altered in some way maybe it triggers the exception. Dunno. But as Philho mentioned, the problem must be lying outside the code you show here...
	Yiannis Chatzikonstantinou volatile prototypes

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