union of two file with array

[onurmimar]

Sorry for my bad language.

I am beginner of Java.

This is my approach:

I am trying to read two files and then get the union of them. I should use an array with size 100. (just one array allowed)

First, I read all records from file1, and write them to the output, a third file. For that purpose, I read 100 record at a time, and write them to the third file using iteration.

After that, like first file, this time I read second file as 100 records at a time, and write them to the array, memory[]. Then I find the common records, if the record which I read from File2 is not in File1, I write it to the output file. I do this until reader2.readLine() gets null and I re-open File1 in each iteration.

This is what I have done so far, almost done, bu it gives null pointer exception. Any help would be appreciated.


exception line: while(!line11.equals(memory[k]))

import java.io.*;

public class FileUnion
{
    private static long startTime, endTime;

    public static void main(String[] args) throws IOException 
    {
        System.out.println("PROCESSING...");
        reset();
        startTimer();

        String[] memory = new String[100];
        int memorySize = memory.length;

        File file1 = new File("stdlist1.txt");
        BufferedReader reader1 = new BufferedReader(new FileReader(file1));

        File file3 = new File("union.txt");
        BufferedWriter writer = new BufferedWriter(new FileWriter(file3));

        String line1 = null;

        String line11 = null;


        while((line1 = reader1.readLine()) != null)
        {
            for (int i = 0; i < 100; )
            {
                memory[i] = line1;
                i++;

                if(i < 100)
                {
                    line1 = reader1.readLine();
                }
            }

            for (int i = 0; i < 100; i++)
            {
                writer.write(memory[i]);
                writer.newLine();
            }
        }

        reader1.close();

        File file2 = new File("stdlist2.txt");
        BufferedReader reader2 = new BufferedReader(new FileReader(file2));

        String line2 = null;
        while((line2 = reader2.readLine()) != null)
        {
            for (int i = 0; i < 100; i++)
            {
                memory[i] = line1;
                i++;

                if(i < 100)
                {
                    line2 = reader2.readLine();
                }
            }

            for (int k = 0; k < 100; k++ )
            {
                boolean found = false;
                File f1 = new File("stdlist1.txt");
                BufferedReader buff1 = new BufferedReader(new FileReader(f1));


                while(((line11 = buff1.readLine()) != null) && found == false)
                {

                    while(!line11.equals(memory[k]))
                    {
                        line11 = buff1.readLine();
                    }

                    if(line11.equals(memory[k]))
                    {
                        found = true;
                    }
                    else
                    {
                        writer.write(memory[k]);
                    }
                }

                buff1.close();

            }
        }

        reader2.close();
        writer.close();

        endTimer();
        long time = duration();
        System.out.println("PROCESS COMPLETED SUCCESSFULLY");
        System.out.println("Duration: " + time + " ms");

    }

    public static void startTimer()
    {
        startTime = System.currentTimeMillis();
    }
    public static void endTimer()
    {
        endTime = System.currentTimeMillis();
    }
    public static long duration()
    {
        return endTime - startTime;
    }
    public static void reset()
    {
        startTime = 0;
        endTime = 0;
    }
}