Working on a fairly simple probgram... the portions that I think are relevant are below.

bauercalc.pde
Code:

int nProb = 0;
Problem[] allProblems;

int i=0;
int j=0;
int k=0;
int l=0;


void setup(){
  //load problems file
  String rawProbList[] = loadStrings("problems.txt");
  String thisLine;
  for(i=0;i < rawProbList.length; i++){
    //above reads each line.  logic follows..
    thisLine = rawProbList[i];
    
    //is it a comment?
    if((thisLine.length() < 2) || (thisLine.substring(0,2).equals("//") == false)){
	//it's not a comment
	//Is it a header?
	if(thisLine.equals("HEADER") == true){
	  j=0;
	  //First "line" of the problem
	  //Also update the count of valid lines...
	  nProb++;
	}else{
	  //it's a content line, not header
	  switch(j){
	    case 0:
		//need to make a new problem; this line gives the filename
		allProblems = (Problem[])append(allProblems, new Problem(thisLine));
		break;
	    case 1:
		//update topic of this problem...
		allProblems[nProb-1].topic = int(thisLine);
		break;
	    case 2:
		//update DC this problem...
		allProblems[nProb-1].level = int(thisLine);
		break;
	    case 3:
		//update answer of this problem...
		allProblems[nProb-1].answer = thisLine.charAt(0);
		break;
	  }
	  //increment which one we're on
	  j++;
	}
    }//end of dealing with a valid line
    
  }//end of reading problems.txt
 

problemObj.pde
Code:

class Problem
{
  //class representing the current problem
  char answer;
  int topic;
  int level;
  String fileName;
  PImage visual;
  
  void display(int ecks, int why){
    //draw it
    image(visual, ecks, why);
  }
  
  Problem(String ifileName){
    fileName = ifileName;
    //load it
    visual = loadImage(fileName);
  }
} 

I'm getting a NullPointerException, with output as follows:

Code:

Exception in thread "Animation Thread" java.lang.NullPointerException
	at java.lang.reflect.Array.getLength(Native Method)
	at processing.core.PApplet.append(PApplet.java:4691)
	at bauercalc.setup(bauercalc.java:92)
	at processing.core.PApplet.handleDraw(PApplet.java:1383)
	at processing.core.PApplet.run(PApplet.java:1311)
	at java.lang.Thread.run(Unknown Source) 

I've had to deal with several NullPointerExceptions from syntax issues, but they all highlighted a specific line.  This has no line reference... and the error still occurs when I replace thisLine.length() and rawProbList.length with constants.

Any thoughts?  I'm afraid I'm new at both Processing and Java... any advice or aid would be appreciated!

Thanks for the prompt help!

BenHem: I'm pretty sure the nProb-1 isn't an issue.  I tried initialising it as Code:

int nProb =1; 

and still got the error.  It should never be a problem anyway- the file that I'm reading from has a very strict syntax, and any line that would call that switch(j) statement will come after a HEADER line- that is, nProb++ will always be executed before thy switch statement.

PhiLho: Aha!  I've kind of been confused by the array/object initialization styntax- I'm used to PHP, which of course has none of that.  I added Code:

allProblems = new Problem[0]; 

to the toppish section of setup(), and the program at least doesn't crash.  Just to confirm- that will give it an initial length of 0 elements, so it will only contain elements I append()...right?