NullPointerException during run time for unknown reason

Question

I keep getting a NullPointerException every time I run my program and I don't know what to do to get this to work. It is supposed to parse the input file data, do some calculations (all are not coded yet), and then print to an output file.

Here are my classes:

Driver:

public class Driver
{
    public static void main(String[] args) throws IOException
    {
        Analyzer start = new Analyzer();
        start.start();  
    }
}

Analyzer:

public class Analyzer 
{
    public void start() throws IOException
    {       
        int total = 0;
        int totalError = 0;
        final int SIZE = 31;
        Response data[] = new Response[SIZE];

        PrintWriter out = new PrintWriter(new FileWriter("apacheOut.txt"));

        Scanner scan = new Scanner (new File("access_log1.txt"));
        while(scan.hasNext())
        {   
            String address = scan.next();
            scan.next(); //garbage line
            scan.next(); //garbage line

            String date = scan.next() + " " + scan.next(); 

            String temp = scan.next();
            String request = temp.substring(1);
            scan.next(); //garbage line

            int status = 0;
            while(status == 0)
            {
                if(scan.hasNextInt())
                    status = scan.nextInt();
                else
                    scan.next(); //garbage line
            }

            int bytes = 0;
            if(status < 300)
            {
                if(scan.hasNextInt())
                {
                    bytes = scan.nextInt();
                }
                else
                {
                    scan.next(); //garbage line
                } 
            }

            String referAgent = scan.nextLine();

            if(status < 400)
            {
                SuccessResponse srp = new SuccessResponse(address, date, request, status, bytes, referAgent);
            }
            else
            {
                ErrorResponse err = new ErrorResponse(address, date, request, status, bytes, referAgent);
                totalError++;
            }

            total++;    
        }

        int numGet = 0;
        int numPost = 0;
        double numBytes = 0;
        for (int i = 0; i <= SIZE; i++)
        {   
            String address = data[i].getAddress();
            String date = data[i].getDate();
            String request = data[i].getRequest();
            int status = data[i].getStatus();
            int bytes = data[i].getBytes();
            String referAgent = data[i].getReferAgent();

            /** GET/POST count */
            if (request.substring(0,1) == "G")
            {   
                numGet++;
            }
            else if (request.substring(0,1) == "P")
            {
                numPost++;
            }

            /** Number of total bytes */
            numBytes = bytes++;
        }

        out.println ("Warren Smith's Results");
        out.println ("======================");
        out.println ("The total number of requests in the file: " + total);
        out.println ("The total number of GET requests: " + numGet);
        out.println ("The total number of POST requests: " + numPost);
        out.println ("The total number of bytes served: " + numBytes);
        out.println ("The number & percentage of pages producing various status categorizations:" );
        out.println ("    1xx Informational: ");
        out.println ("    2xx Status: ");
        out.println ("    3xx Redirection: ");
        out.println ("    4xx Client Error: ");
        out.println ("    5xx Server Error: ");
        out.println ("The percentage and number of Windows-based clients: ");
        out.println ("The percentage and number of bad requests: " + totalError);
        out.println ("The percentage and number of clients that are Mozilla-based: ");
        out.println ("The percentage and number of requests from the Googlebot: ");

        out.close();
    }
}

Response:

abstract public class Response 
{
    protected String address;
    protected String date;
    protected String request;
    protected int status;
    protected int bytes;
    protected String referAgent;

    /** Response object constructor */
    public Response (String eAddress, String eDate, String eRequest, int eStatus, int eBytes, String eReferAgent)
    {
        address = eAddress;
        date = eDate;
        request = eRequest;
        status = eStatus;
        bytes = eBytes;
        referAgent = eReferAgent;
    }

    /** Returns the IP address */
    public String getAddress()
    {
        return address;
    }

    /** Returns the date */
    public String getDate()
    {
        return date;
    }

    /** Returns the request to server */
    public String getRequest()
    {
        return request;
    }

    /** Returns the status code */
    public int getStatus()
    {
        return status;
    }   

    /** Returns the # of bytes */
    public int getBytes()
    {
        return bytes;
    }

    /** Returns the referring page & agent */
    public String getReferAgent()
    {
        return referAgent;
    }
}

SuccessResponse:

public class SuccessResponse extends Response
{
    /** SuccessResponse object constructor */
    public SuccessResponse (String eAddress, String eDate, String eRequest, int eStatus, int eBytes, String eReferAgent)
    {
        super (eAddress, eDate, eRequest, eStatus, eBytes, eReferAgent);
    }

    /** Returns the IP address */
    public String getAddress()
    {
        return address;
    }

    /** Returns the date */
    public String getDate()
    {
        return date;
    }

    /** Returns the request to server */
    public String getRequest()
    {
        return request;
    }

    /** Returns the status code */
    public int getStatus()
    {
        return status;
    }   

    /** Returns the # of bytes */
    public int getBytes()
    {
        return bytes;
    }

    /** Returns the referring page */
    public String getReferAgent()
    {
        return referAgent;
    }
}

ErrorResponse:

public class ErrorResponse extends Response
{
    /** ErrorResponse object constructor */
    public ErrorResponse (String eAddress, String eDate, String eRequest, int eStatus, int eBytes, String eReferAgent)
    {
        super (eAddress, eDate, eRequest, eStatus, eBytes, eReferAgent);
    }

    /** Returns the request to server */
    public String getRequest()
    {
        return request;
    }

    /** Returns the status code */
    public int getStatus()
    {
        return status;
    }   

    /** Returns the # of bytes */
    public int getBytes()
    {
        return bytes;
    }

    /** Returns the referring page */
    public String getReferAgent()
    {
        return referAgent;
    }
}

The output for this is:

[java] Exception in thread "main" java.lang.NullPointerException
[java]     at Analyzer.start(Unknown Source)
[java]     at Driver.main(Unknown Source)
[java] Java Result: 1

Any ideas why the NullPointerException keeps coming up?

Answer 1

It seems that elements inside data array are not initialized, but you try to call methods using them.