FireSimulation Program, got stuck with a bug...

[riz618]

Hi EveryOne,

I am writing a java application called FireSimulation and a I have a bug which needs to be resolved. I will appreciate your help. The code for the following is below.

GRID>JAVA

package Fire.Simulation.riz;

import java.util.Scanner;

public class Grid extends Cell {
public int probablityTree;
public int probablityFire;
boolean willGenerateTree;
boolean willCatchFire;
public double r;
public Cell[][] Box;

public Grid(int rows,int columns)
{
willGenerateTree = false;
willCatchFire = false;
Box= new Cell[rows][columns];

for(int i=0;i<rows;i++)
{
for(int j=0;j<columns;j++)
{
System.out.println("first for");
Box=new Cell[i][j];
}
System.out.println("Second for");
}

}

public void GenerateGrid() {

}

public void ProbTree()
{
for(int i=0;i<(Box.length-1);i++)
{
for(int j=0;j<(Box[0].length-1);j++)
{
r=Math.random();
if(r>0 && r<=probablityTree)
willGenerateTree=true;
r=Math.random();
if(r>0 && r<=probablityFire)
willCatchFire=true;

if(willGenerateTree)
{
if(willCatchFire)
{
Cell[i][j].setState(2);
}
else
{
Cell[i][j].setState(1);
}
}
else
{
Cell[i][j].setState(0);
}
}


}

}

public static void main(String args[])
{
int row, column;
Scanner scan = new Scanner(System.in);
System.out.println("Please enter the number of rows :");
row=scan.nextInt();
System.out.println("Please enter the number of columns :");
column=scan.nextInt();
Grid g = new Grid(row,column);
g.ProbTree();


}


}


Cell.java

package Fire.Simulation.riz;

public class Cell {

public int State;
public int s;

public Cell()
{

}

public int getState() {
return s;
}

public void setState(int s) {
this.s = s;
}

}


The bug is highlited here,

[jelly]

You should be refering to the name of your variable - Box, i.e. channge

Code:

Cell[i][j].setState(2)

to read

Code:

Box[i][j].setState(2)

[riz618]

Even if i change to that, i get the following errors

Exception in thread "main" java.lang.NullPointerException
at Fire.Simulation.riz.Grid.ProbTree(Grid.java:62)
at Fire.Simulation.riz.Grid.main(Grid.java:80)

So there has to be something that needs a fix, if this is right.

Thanks for replying

[jelly]

your second problem is with the initialisation of your array, your constructor for grid has the variable and the class ( Box and Cell) slightly confused, i.e. you wrote

Code:

Box=new Cell[i][j];

should be

Code:

Box [i][j]=new Cell();

so that every entry in the two dimensional array gets allocated a new Cell object - actually I'm surprised the code as posted compiles

[riz618]

still did not solve my problem, if you could do me a fovour, compile the files i have provided and see if it works for you. That way you will have a better idea of what i am dealing with.

Thanks

[jelly]

Having made the changes as said above, it runs fine, output:

Code:

Jackdaw:$ javac Grid.java
Jackdaw:$ java Grid
Please enter the number of rows :
4
Please enter the number of columns :
3
first for 
first for 
first for
Second for 
first for 
first for 
first for 
Second for 
first for 
first for 
first for 
Second for 
first for 
first for 
first for 
Second for 
Jackdaw:$

code I ran

Code:

import java.util.Scanner;

public class Grid extends Cell {
public int probablityTree;
public int probablityFire;
boolean willGenerateTree;
boolean willCatchFire;
public double r;
public Cell[][] Box;

public Grid(int rows,int columns) 
{
willGenerateTree = false;
willCatchFire = false;
Box= new Cell[rows][columns];

for(int i=0;i<rows;i++)
{
for(int j=0;j<columns;j++)
{
System.out.println("first for "+i+"**"+j);
Box[i][j]=new Cell();
}
System.out.println("Second for "+i+"**");
}

}

public void GenerateGrid() {

}

public void ProbTree()
{
for(int i=0;i<(Box.length-1);i++)
{
for(int j=0;j<(Box[0].length-1);j++)
{
r=Math.random();	
if(r>0 && r<=probablityTree)
willGenerateTree=true;
r=Math.random();
if(r>0 && r<=probablityFire)
willCatchFire=true;

if(willGenerateTree)
{
if(willCatchFire)
{
Box[i][j].setState(2);
}
else
{
Box[i][j].setState(1);
}
}
else
{
Box[i][j].setState(0);
}
}	


}	

}

public static void main(String args[])
{
int row, column;
Scanner scan = new Scanner(System.in);
System.out.println("Please enter the number of rows :");
row=scan.nextInt();
System.out.println("Please enter the number of columns :");
column=scan.nextInt();
Grid g = new Grid(row,column);
g.ProbTree();


}

public class Cell {

public int State;
public int s;

public Cell()
{

}

public int getState() {
return s;
}

public void setState(int s) {
this.s = s;
}

}