Nullpointer Exception problem

[shanaya dutt]

in the following program I get a Nullpointer exception at line 96.the program reads a large list of values from a file and puts them into an array.the file does not contain any null values.pl,ease help me with this code

  
import java.io.*;
import java.awt.*;
import java.awt.geom.*;
import java.awt.geom.Arc2D.*;
import javax.swing.*;
import java.lang.Double; 


class mpplot

{	static double average;
	
	static int numofmp=0;
	static double array[];
public static void main(String args[]) throws IOException
{
	String line;
	double array1[]=new double[800000];

   try{	File file=new File(args[0]);
	final BufferedReader br = new BufferedReader(new FileReader(file));
	
	double z=0;
	
	while((line=br.readLine())!=null)
   { 	
	if(line==null) break;
	try{
 	z = Double.parseDouble(line.trim());
	array1[numofmp]=z;
	numofmp++;
	}catch(Exception e1)
	{System.out.println(e1.getMessage());}
	
   }
  }catch(Exception e2)
	{System.out.println(e2.getMessage());}
	double array[]=new double[numofmp];
	
	for(int i=0;i<array.length;i++)
	{array[i]=array1[i];
	//System.out.println(array[i]);
	}
	
	double result;
	result=0.0;
	for(int i=0;i<array.length;i++)
	{result+=array[i];}
	average=result/(array.length);
	System.out.println(numofmp);
	System.out.println("average"+average);

	JFrame frame=new JFrame("mp");
	frame.add(new plotter());
	frame.pack();
	frame.setSize(1200,1200);
    	frame.setVisible(true);
    	frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

}//psvm

}//end class







class plotter extends JComponent
{
	
	 final double  X_CENTER = 400;
    	final double Y_CENTER = 300;
	 double x,y;
	public void paint(Graphics g)
	{

	mpplot obj=new mpplot();
	 Graphics2D g2=(Graphics2D)g;
	double	radius4= 150.0f;
	int numpix4=obj.numofmp;
	double mparr[]=obj.array;
	double angle4,anginc4;

	 anginc4 = (double) (2.0 * Math.PI / numpix4);
	
	int j=0;
	for (angle4 = 0.0f; angle4 < 2.0 * Math.PI; angle4 += anginc4)
        {  
            x = X_CENTER + (int) (radius4 * Math.cos(angle4));
            y = Y_CENTER + (int) (radius4 * Math.sin(angle4));
	   
	   g2.setColor(Color.green);
			
		if(mparr[j]<obj.average+2.5){
                    g2.setColor(Color.blue);
		}else{
		if(mparr[j]>obj.average-2.5)
		{g2.setColor(Color.gray);}	}
		g2.setStroke(new BasicStroke(5.0f));	
            g2.draw(new Line2D.Double(x, y,x, y));
    		j++;
        }
	
   


	}//end paint
	




}//end class
  

[Ankit Garg]

Can you point out the line where the exception is coming. Line number 96 in your code is empty...

[shanaya dutt]

line 97...it may occur at 100 too

[Rob Spoor]

mparr is null, because you never give it any value.

And with "it" I don't mean mparr itself but mpplot's array field.

[shanaya dutt]

i did the following modification but it still throws an exception.Now at mparr assignment part at line 88.where am i going wrong?

   
import java.io.*;
import java.awt.*;
import java.awt.geom.*;
import java.awt.geom.Arc2D.*;
import javax.swing.*;
import java.lang.Double; 


class mpplot

{	static double average;
	
	static int numofmp=0;
	static double array[];
public static void main(String args[]) throws IOException
{
	String line;
	double array1[]=new double[800000];

   try{	File file=new File(args[0]);
	final BufferedReader br = new BufferedReader(new FileReader(file));
	
	double z=0;
	
	while((line=br.readLine())!=null)
   { 	
	if(line==null) break;
	try{
 	z = Double.parseDouble(line.trim());
	array1[numofmp]=z;
	numofmp++;
	}catch(Exception e1)
	{System.out.println(e1.getMessage());}
	
   }
  }catch(Exception e2)
	{System.out.println(e2.getMessage());}
	double array[]=new double[numofmp];
	
	for(int i=0;i<array.length;i++)
	{array[i]=array1[i];
	//System.out.println(array[i]);
	}
	
	double result;
	result=0.0;
	for(int i=0;i<array.length;i++)
	{result+=array[i];}
	average=result/(array.length);
	System.out.println(numofmp);
	System.out.println("average"+average);

	JFrame frame=new JFrame("mp");
	frame.add(new plotter());
	frame.pack();
	frame.setSize(1200,1200);
    	frame.setVisible(true);
    	frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

}//psvm

}//end class







class plotter extends JComponent
{
	
	 final double  X_CENTER = 400;
    	final double Y_CENTER = 300;
	 double x,y;
	public void paint(Graphics g)
	{

	mpplot obj=new mpplot();
	 Graphics2D g2=(Graphics2D)g;
	double	radius4= 150.0f;
	int numpix4=obj.numofmp;
	double mparr[]=new double[numpix4];
	double angle4,anginc4;
	for(int i=0;i<mparr.length;i++)
	{
	mparr[i]=obj.array[i];
	}
	 anginc4 = (double) (2.0 * Math.PI / numpix4);
	
	int j=0;
	for (angle4 = 0.0f; angle4 < 2.0 * Math.PI; angle4 += anginc4)
        {  
            x = X_CENTER + (int) (radius4 * Math.cos(angle4));
            y = Y_CENTER + (int) (radius4 * Math.sin(angle4));
	   
	   g2.setColor(Color.green);
			
		if(mparr[j]<obj.average+2.5){
                    g2.setColor(Color.blue);
		}else{
		if(mparr[j]>obj.average-2.5)
		{g2.setColor(Color.gray);}	}
		g2.setStroke(new BasicStroke(5.0f));	
            g2.draw(new Line2D.Double(x, y,x, y));
    		j++;
        }
	
   	}//end paint
	

}//end class


 

[Rob Spoor]

You still never assign the array field. You create two double arrays, sure, but those are method local variables.

[shanaya dutt]

okay!!
But then whats wrong with this code.Here i'm directly accessing the array from the mpplot class.it still throws the exception at the comparison in paint.

  import java.io.*;
import java.awt.*;
import java.awt.geom.*;
import java.awt.geom.Arc2D.*;
import javax.swing.*;
import java.lang.Double; 


class mpplot

{	static double average;
	
	static int numofmp=0;
	static double array[];
public static void main(String args[]) throws IOException
{
	String line;
	double array1[]=new double[800000];

   try{	File file=new File(args[0]);
	final BufferedReader br = new BufferedReader(new FileReader(file));
	
	double z=0;
	
	while((line=br.readLine())!=null)
   { 	
	if(line==null) break;
	try{
 	z = Double.parseDouble(line.trim());
	array1[numofmp]=z;
	numofmp++;
	}catch(Exception e1)
	{System.out.println(e1.getMessage());}
	
   }
  }catch(Exception e2)
	{System.out.println(e2.getMessage());}
	double array[]=new double[numofmp];
	
	for(int i=0;i<array.length;i++)
	{array[i]=array1[i];
	//System.out.println(array[i]);
	}
	
	double result;
	result=0.0;
	for(int i=0;i<array.length;i++)
	{result+=array[i];}
	average=result/(array.length);
	System.out.println(numofmp);
	System.out.println("average"+average);

	JFrame frame=new JFrame("mp");
	frame.add(new plotter());
	frame.pack();
	frame.setSize(1200,1200);
    	frame.setVisible(true);
    	frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

}//psvm

}//end class







class plotter extends JComponent
{
	
	 final double  X_CENTER = 400;
    	final double Y_CENTER = 300;
	 double x,y;
	public void paint(Graphics g)
	{

	mpplot obj=new mpplot();
	 Graphics2D g2=(Graphics2D)g;
	double	radius4= 150.0f;
	int numpix4=obj.numofmp;
	
	double angle4,anginc4;
	
	 anginc4 = (double) (2.0 * Math.PI / numpix4);
	
	int j=0;
	for (angle4 = 0.0f; angle4 < 2.0 * Math.PI; angle4 += anginc4)
        {  
            x = X_CENTER + (int) (radius4 * Math.cos(angle4));
            y = Y_CENTER + (int) (radius4 * Math.sin(angle4));
	   
	   g2.setColor(Color.green);
			
		if(obj.array[j]<obj.average+2.5){
                    g2.setColor(Color.blue);
		}else{
		if(obj.array[j]>obj.average-2.5)
		{g2.setColor(Color.gray);}	}
		g2.setStroke(new BasicStroke(5.0f));	
            g2.draw(new Line2D.Double(x, y,x, y));
    		j++;
        }
	
   


	}//end paint
	




}//end class
  

[Rob Spoor]

shanaya dutt wrote:

static double array[];

Where do you give it a value? The answer: nowhere. Therefore, it will remain null.