Thread: 2 dimentional boolean array problems!

Hi


How can I do a matrix code with a boolean expression and then output it?

I know that when you declare a 2 dimensional boolean array that all the elements are already false. So how can I display them elements that are false with a '.' and if true with a 'O'?

Sorry for the dumb amateur question but I just cant do it!

Thank you for any help given!

I have tried this:

 
	{
		       for(int i=0;i<matrix.length;i++)
		       {
		          for(int j=0;j<matrix[i].length;j++)
		          {
		             if(matrix[i][j])
		             {
		               System.out.print("O");
		             }
		             else
		             {
		               System.out.print(".");
		             }
		          }
		            System.out.println("");

How ever the problem here is that I get a nullPointerException error appear.

The full code is:

/**
 * Class LEDDisplay - write a description of the class here.
 * 
 * @author (your name) 
 * @version (a version number or a date)
 */
public class LEDDisplay
{
	/* private class constants */
	private final int FONT_LETTER_HEIGHT = 5;
	private final int FONT_LETTER_WIDTH = 6;
	private final int LETTERS_PER_DISPLAY = 10;
 
 
	/* instance variables */
	private boolean [][] matrix;
 
	/**
	 * Constructor for objects of class LEDDisplay
	 */
	public LEDDisplay()
	{
		boolean[][] matrix = new boolean [FONT_LETTER_HEIGHT] [FONT_LETTER_WIDTH * LETTERS_PER_DISPLAY];
	}
 
	/*
	 * This display() method will print a textual representation of matrix[][] onto the display pane.
	 */
 
	public void display()
 
	{
		       for(int i=0;i<matrix.length;i++)
		       {
		          for(int j=0;j<matrix[i].length;j++)
		          {
		             if(matrix[i][j])
		             {
		               System.out.print("O");
		             }
		             else
		             {
		               System.out.print(".");
		             }
		          }
		            System.out.println("");
 
}
	}
}

I think that I need to add something to do with a 'char' >? But I am a complete amateur and have no idea where to sort this out!

I just want to to output a display like this:
.................................................. .................................................. ......................................
.................................................. .................................................. ......................................
.................................................. .................................................. ......................................
.................................................. .................................................. ......................................
.................................................. .................................................. ......................................

at this stage as each '.' represents a false value in that 2 dim array.

I also think that its something to do with the fact that I have declared matrix twice? Again I still have no idea how I can sort it!?

The error I get at this stage is:
Exception: line 2. java.lang.NullPointerException

Which is crazy as line 2 is fine!

I have been going crazy for weeks on this and what annoys me is that its such a simple thing! Please help me before I go crazy !

Again thank you for any help you give on this!

Regards