NullPointerException in a double loop

[Bloitz]

Hello fellow javanians,

Breaking my head over this method for the last 3 hours. I'm getting a NullPointerException in this double loop. I know it's coming from lblEmpty[row][col] in pnlBoard.add(lblEmpty[row][col]); because I changed it with a testlabel (one that wasn't created in the loop) and it worked...

Scenario: I have to get a predesigned gameboard from a DB (works because I first did it with a JTextPane and copied the displayBoard method from our working ConsoleApplication) and display it in my GUI. So I made a JPanel to house the gameboard and made a double loop to add JLabels according to the size of the gameboard in the DB.

Error comes from pnlBoard.add(lblEmpty[row][col]); where lblEmpty[row][col] doesn't seem to exist according to Java (and Java tends to be right a lot).
Here's my loop:

private JLabel lblEmpty[][];
private JPanel pnlBoard;


//loads of other, unrelated code

initGUI(){
// loads of other, unrelated code
getContentPane().add(displayBoard());
}

private JPanel displayBoard()
	{
		String[][] spelbord=domeinController.startSpel();
		
		GridLayout grid = new GridLayout(spelbord.length, spelbord[0].length, 2, 2);
		pnlBoard = new JPanel();
		pnlBoard.setLayout(grid);
		pnlBoard.setBounds(20,20,500,420);
		
		lblEmpty = new JLabel[spelbord.length][spelbord[0].length];
		for(int row=0;row<spelbord.length;row++)
		{
			for(int col=0;col<spelbord[row].length;col++)
			{
				if(row == spelbord.length -2 && col == spelbord.length -2){
					lblFinish = new JLabel("FINISH");
					pnlBoard.add(lblFinish);
				}
				else
					lblEmpty[row][col] = new JLabel("X");
					pnlBoard.add([COLOR="red"]lblEmpty[row][col][/COLOR]);
			}
		}
		return pnlBoard;
	}

As far as I can tell there's nothing wrong with this loop aside from not creating the lblEmpty ...

If you'd like more info, please feel free to ask.

Kind regards, Bloitz

PS: Dutch ==> English translations if its any help:
spelbord = gameboard
domeinController = domainController

[dlorde]

You've declared and created a 2D array that can hold a table of JLabels, but you haven't put any JLabels into it, so all the entries will be null references.

[Bloitz]

Thank you for your reply

I created a second double loop filling up the 2D array and it works. it just seems a lot of code for something small ... :)

Solution 1: Filling up the 2D array first:

private class BoardPanel extends JPanel{
		
		private JLabel lblEmpty[][], lblFinish;
		
		public BoardPanel(){
			super();
			displayBoard();
		}
		private void displayBoard()
		{
			String[][] spelbord=domeinController.startSpel();
			
			GridLayout grid = new GridLayout(spelbord.length, spelbord[0].length, 2, 2);
			setLayout(grid);
			setSize(500,420);
			
			[COLOR="RoyalBlue"]{
				lblEmpty = new JLabel[spelbord.length][spelbord[0].length];
				for(int row=0;row<spelbord.length;row++)
				{
					for(int col=0;col<spelbord[row].length;col++)
					{
						lblEmpty[row][col] = new JLabel("X");
					}
				}
			}[/COLOR]
			for(int row=0;row<spelbord.length;row++)
			{
				for(int col=0;col<spelbord[row].length;col++)
				{
					if(row == spelbord.length -2 && col == spelbord.length -2){
						lblFinish = new JLabel("FINISH");
						this.add(lblFinish);
					}
					else
						this.add(lblEmpty[row][col]);
				}
			}
		}
	}

Solution2: Creating an Innerclass within an innerclass of the JFrameclass (no, this isn't a sneaky Inception refrence although the movie is pretty good :) )

private class BoardPanel extends JPanel{
		
		private JLabel lblFinish, lblObst, lblPlayer;
		[COLOR="RoyalBlue"]private LblEmpty lblEmpty;[/COLOR]
		
		public BoardPanel(){
			super();
			displayBoard();
		}
		private void displayBoard()
		{
			String[][] spelbord=domeinController.startSpel();
			
			GridLayout grid = new GridLayout(spelbord.length, spelbord[0].length, 2, 2);
			setLayout(grid);
			setSize(500,420);
			
			for(int row=0;row<spelbord.length;row++)
			{
				for(int col=0;col<spelbord[row].length;col++)
				{
					if(row == spelbord.length -2 && col == spelbord.length -2){
						lblFinish = new JLabel("FINISH");
						this.add(lblFinish);
					}
					else
						[COLOR="RoyalBlue"]lblEmpty = new LblEmpty();[/COLOR]
						this.add(lblEmpty);
				}
			}
		}
		
		[COLOR="RoyalBlue"]private class LblEmpty extends JLabel{
			public LblEmpty(){
				super("");
				this.setBackground(getContentPane().getBackground());
				this.setBorder(BorderFactory.createLineBorder(Color.white));
			}
		}[/COLOR]
	}

+ rep'ed even though it's obvious now I think of it. :)

PS: I always get this error when clicking 'Mark as solved' in the thread tools. It does however mark it as solved when I check back. I use Google Chrome version 11.0.696.65: http://i.imgur.com/L0kJs.jpg