Java OOP Help - Saddle Point

[JonB]

Before I get into the problem I'd like to state that I am NOT looking for someone to complete my assignment for me, I'm just after a little bit of guidance.

I'm stuck with some OOP in java. It's my first ever class/package in java and it all compiles but running it doesn't go so well:

Basically the challenge is to generate a grid, of X size, display it and then work out where the saddle point is. The problem I am having though, at the moment, is generating the grid.

Source Code : http://www.imgholder.co.uk/files/1/Assignment6.zip

There is no stipulation that this had to be written with a class, I just wanted to challenge myself, so if worst comes to worst I can revert back to a procedural version.

Does anyone have any ideas as to why I am getting the error in above screenshot?

 

[Dj_Jestar]

NullPointerException indicates you are trying to make a null value do something. The below example would compile, but throw a null pointer exception when run.

String variable;
variable.indexOf('x'); //String is still null at this point

Also, as an FYI/Tip, when looking at the stack trace (which is what you have taken a screeny of) only ever worry about the top most error before fixing others.

 

[Fourstar]

From the stack trace we can see that the NullPointerException was raised on line 47 of Grid.java in the method createGrid.

That line is:

grid[row][col] = generator.nextInt(10);

row and column look fine, no idea what generator is so I'll check "grid" first.

This is declared at the top of your class as:

private int grid[][];

I can't see anywhere in the class where you instantiate the object before using it.

I can't remember the Java syntax but is something like:

grid = New int[gridSize][gridSize];

You get the idea