More trouble with classes and arrays

[CuddlyKittens11]

Okay, I got this file:
globals.java:

public class globals {
	static public frame frames[] = new frame[maxFramesAllowed];		// Holds the grid data, maximum of 1000 frames right now
	
	static public class frame {
		public cell cells[] = new cell[maxCellsAllowed];
		public char nextFreeCell = 0;
		public char delay = 1;
		
		public frame() {
			// nothing
		}
		
		public frame(int frameDelay) {
			delay = (char) frameDelay;
		}
		
		public frame(char frameDelay) {
			delay = frameDelay;
		}
	}
	
	static public class cell {
		public char x;
		public char y;
		public char value;
		
		public cell(int xVal, int yVal, int val) {
			x = (char) xVal;
			y = (char) yVal;
			value = (char) val;
		}
		
		public cell(char xVal, char yVal, char val) {
			x = xVal;
			y = yVal;
			value = val;
		}
	}
}

When I ran it with the regular portion of my program, I got errors about null pointers/objects.

So iIcreated this program to test the class:
TEST_globals.java

public class TEST_globals {
	public globals g;
	
	public static void main(String argv[]) {
		for (int i = 0; i < 5; i++) {
			globals.frames[i] = new globals.frame(i * 2);
			System.out.println("Delay for frame[" + i + "]: " + globals.frames[i].delay);
			
			for (int j = 0; j < 5; j++) {
				System.out.println("\tFor frame[" + i + "], next free cell at[" + globals.frames[i].nextFreeCell + "]");
				globals.frames[i].cells[globals.frames[i].nextFreeCell] = new globals.cell(j, j, i * j);
				globals.frames[i].nextFreeCell++;
			}
		}
	}
}

The result:


Please help. :(

[sunde887]

Before I read and respond I just wanted to point out that you forgot the [ code] part of your first snippet.

Also, I am not really sure what you are asking, would you mind clarifying your question for me?

[CuddlyKittens11]

What I want is for my data, when I access it, not to turn up as a "null", as it is doing right now.

[sunde887]

Others may have better advice, but are you adding information to the cells?

[CuddlyKittens11]

Yeah, I am going to, but I'm trying to fix the issue with the null data first.

[sunde887]

If you try to access an array element before you fill it you will get a null pointer exception. If you create the array and don't fill the array and try to do anything with the items in the array, it will cause a null pointer exception. Can you show me the code that generate the null pointer exception and the stack trace?

[CuddlyKittens11]

You mean this, I also have declared in "globals.java":

static public int maxFramesAllowed = 10;    // Small right now for simplicity
static public frame frames[] = new frame[maxFramesAllowed];

[sunde887]

A stack trace looks something like this

Exception in thread "main" java.lang.NullPointerException
        at TestArray.main(testarray.java:5)

And lets us see what causes the problems. Is the above the code that was giving you null errors?

Normally when you get a null error it's cause by trying to do something on an object that hasn't been instantiated. Here is a small example I created which causes a NullPointerException

public class TestArray{
	public static void main(String[] args){
		Object[] x = new Object[5];
		for(int i = 0; i < x.length; ++i){
			System.out.println(x[i].toString());
		}
	}
}

To avoid null pointers you need to fill the array. In the above example you would do something like this

public class TestArray{
	public static void main(String[] args){
		Object[] x = new Object[5];
                for(int i = 0; i < x.length; ++i){
                        x[i] = new Object();
                }
		for(int i = 0; i < x.length; ++i){
			System.out.println(x[i].toString());
		}
	}
}

From the fact that you are receiving null pointer exceptions, I am assuming you are attempting to call methods on an array with items that have not been initialized. Like I said, this is an assumption.

[kjkrum]

You mean this, I also have declared in "globals.java":

static public int maxFramesAllowed = 10;    // Small right now for simplicity
static public frame frames[] = new frame[maxFramesAllowed];

So what you have there is an array of 10 references to frame objects. Each one of those references is null. You have to fill the array, like this:

for(int i = 0; i < frames.length; ++i)
     frames[i] = new frame(...);

BTW... it'll be very helpful to you later, as well as helpful to anyone reading your code, if you adopt the standard Java conventions for naming and capitalization.

[CuddlyKittens11]

Hey guys, I figured out my problem, it had something to do with the char datatypes I was using.

Thanks though.