Read multiple files and save all into one output file(AGAIN)

Question

Hi, guys
I need your help for reading data from multiple files and save the results into one output file. When files are selected from file chooser, my program read the data line by line , do some calculations and save the result into the output. I made an array to store input files and it seems to be working fine, but when it comes to SaveFile() function, issues NullPointException message.
public class FileReduction1 extends JFrame implements ActionListener
   // GUI definition and layout
    /* ACTION PERFORMED */
    public void actionPerformed(ActionEvent event) {
        if (event.getActionCommand().equals("Open File")) getFileName();
    /* OPEN THE FILE */
    private void getFileName() {
        // Display file dialog so user can select file to open
     JFileChooser fileChooser = new JFileChooser();
     fileChooser.setFileSelectionMode(JFileChooser.FILES_ONLY);
        fileChooser.setMultiSelectionEnabled(true);
     int result = fileChooser.showOpenDialog(this);
     // If cancel button selected return
     if (result == JFileChooser.CANCEL_OPTION) return;
        if (result == JFileChooser.APPROVE_OPTION)
         files = fileChooser.getSelectedFiles();
            textArea.setText("");
            if(files.length>0)
                filelist="";
                System.out.println("files length"+files.length);
                for(int i=0;i<files.length;i++)
                     System.out.println(files.getName());
filelist+=files[i].getName()+" ,";
if (checkFileName(files[i]) )
openButton.setEnabled(true);
readButton.setEnabled(true);
textArea.append("file "+files[i].getName()+"is a proper file"+"\n");
readFile(files[i]);
textfield.setText(filelist);
else{JOptionPane.showMessageDialog(this,"Please select file(s)",
                "Error 5: ",JOptionPane.ERROR_MESSAGE); }
     // Obtain selected file
/* READ FILE */
private void readFile(File fileName_in) {
// Disable read button
readButton.setEnabled(false);
// Dimension data structure
     getNumberOfLines(fileName_in);
     data = new String[numLines][4];
     // Read file
     readTheFile(fileName_in);
     // Rnable open button
     openButton.setEnabled(true);
/* GET NUMBER OF LINES */
/* Get number of lines in file and prepare data structure. */
private void getNumberOfLines(File fileName_in) {
int counter = 0;
     // Open the file
     openFile(fileName_in);
     // Loop through file incrementing counter
     try {
     String line = fileInput.readLine();
     while (line != null) {
     counter++;
          System.out.println("(" + counter + ") " + line);
line = fileInput.readLine();
     numLines = counter;
closeFile(fileName_in);
     catch(IOException ioException) {
     JOptionPane.showMessageDialog(this,"Error reading File",
               "Error 5: ",JOptionPane.ERROR_MESSAGE);
     closeFile(fileName_in);
     System.exit(1);
/* READ FILE */
private void readTheFile(File fileName_in)
// Open the file
//int row=0;
int col=0;
openFile(fileName_in);
System.out.println("Read the file");
// Loop through file incrementing counter
try
String line = fileInput.readLine();
while (line != null)
boolean containsDoubles = false;
double temp;
String[] lineParts = line.split("\t");
try
for (col=0;col<lineParts.length;col++)
temp=Double.parseDouble(lineParts[col]);
data[row][col] = lineParts[col];
containsDoubles = true;
System.out.print("data["+row+"]["+col+"]="+lineParts[col]+" ");
} catch (Exception e) {row=0; col=0; temp=0.0;}
if (containsDoubles){ row++;}
System.out.println();
line = fileInput.readLine();
catch(IOException ioException)
JOptionPane.showMessageDialog(this,"Error reading File", "Error 5: ",JOptionPane.ERROR_MESSAGE);
closeFile(fileName_in);
System.exit(1);
//System.out.println("length"+data.length);
closeFile(fileName_in);
process(fileName_in);
/* CHECK FILE NAME */
/* Return flase if selected file is a directory, access is denied or is
not a file name. */
private boolean checkFileName(File fileName_in) {
     if (fileName_in.exists()) {
     if (fileName_in.canRead()) {
          if (fileName_in.isFile()) return(true);
          else JOptionPane.showMessageDialog(null,
                    "ERROR 3: File is a directory");
     else JOptionPane.showMessageDialog(null,
                    "ERROR 2: Access denied");
     else JOptionPane.showMessageDialog(null,
                    "ERROR 1: No such file!");
     // Return
     return(false);
/* OPEN FILE */
private void openFile(File fileName_in) {
     try {
     // Open file
     FileReader file = new FileReader(fileName_in);
     fileInput = new BufferedReader(file);
     catch(IOException ioException) {
     JOptionPane.showMessageDialog(this,"Error Opening File",
               "Error 4: ",JOptionPane.ERROR_MESSAGE);
     textArea.append("OPEN FILE\n---------\n");
     textArea.append(fileName_in.getPath());
     textArea.append("\n");
     //System.out.println("File opened successfully");
/* CLOSE FILE */
private void closeFile(File fileName_in) {
if (fileInput != null) {
     try {
          fileInput.close();
     catch (IOException ioException) {
     JOptionPane.showMessageDialog(this,"Error Opening File",
               "Error 4: ",JOptionPane.ERROR_MESSAGE);
System.out.println("File closed");
private void process(File fileName_in) {
//getNumberOfLines();
     //data = new String[numLines][3];
     // Read file
double temp,temp1;
     //readTheFile();
//System.out.println("row:"+row);
//int number=data.length;
//System.out.println(number);
for (int i=0; i<row; i++)
temp=Double.parseDouble(data[i][1]);
sumx+=temp;
temp1=Double.parseDouble(data[i][3]);
sumy+=temp1;
multixy+=(temp*temp1);
square_x_sum+=(temp*temp);
square_y_sum+=(temp1*temp1);
//System.out.println("Sum(x)="+sumx);
double tempup=(row*multixy)-(sumx*sumy);
double tempdown=(row*square_x_sum)-(sumx*sumx);
slope=tempup/tempdown;
double tempbup=sumy-(slope*sumx);
intb=tempbup/row;
double tempside=(row*square_y_sum)-(sumy*sumy);
double cordown=Math.sqrt(tempdown*tempside);
corr=tempup/cordown;
r_sqrt=corr*corr;
     textArea.append("Data for file"+ fileName_in.getName()+" have been processed successfully.");
     textArea.append("\n");
     textArea.append("Please enter output file name including extension.");
System.out.println("number"+row);
System.out.println("slope(m)="+slope);
System.out.println("intecept b="+intb);
System.out.println("correlation="+corr);
System.out.println("correlation="+r_sqrt);
saveFile();
private void saveFile()
textArea.append("SAVE FILE\n---------\n");
if (openFile1())
     try {
          outputToFile();
catch (IOException ioException) {
          JOptionPane.showMessageDialog(this,"Error Writing to File",
               "Error",JOptionPane.ERROR_MESSAGE);
private boolean openFile1 ()
     // search for the file path
StringBuffer stringpath;
title=textfield1.getText().trim();
int temp=fileName_in.getName().length();
int temp_path=fileName_in.getPath().length();
int startd=(temp_path-temp);
stringpath=new StringBuffer(fileName_in.getPath());
stringpath.delete(startd, temp_path+1);
//System.out.println("file-path="+temp_path);
//System.out.println("length-file="+temp);
path=stringpath.toString();
fileName_out = new File(path, title);
//System.out.println(file_out.getName());
if (fileName_out==null || fileName_out.getName().equals(""))
     JOptionPane.showMessageDialog(this,"Invalid File name",
               "Invalid File name",JOptionPane.ERROR_MESSAGE);
     return(false);
     else
try
boolean created = fileName_out.createNewFile();
if(created)
fileOutput = new PrintWriter(new FileWriter(fileName_out));
fileOutput.println("File Name"+"\t"+"Slope(m)"+"\t"+"y-intercept(b)"+"\t"+"Coefficient(r)"+"\t"+"Correlation(R-Squared)");
return(true);
else
fileOutput = new PrintWriter(new FileWriter(fileName_out,true));
return(true);
catch (IOException exc)
JOptionPane.showMessageDialog(this,"Please enter the file name","Error",JOptionPane.ERROR_MESSAGE);
return(false);
private void outputToFile() throws IOException
// Initial output
     textArea.append("File name = " + fileName_out + "\n");
     // Test if data exists
     if (data != null)
     fileOutput.println(fileName_in.getName() +"\t"+ slope+"\t"+intb+"\t"+corr+"\t"+r_sqrt);
textArea.append("File output complete\n\n");
     else
textArea.append("No data\n\n");
     // End by closing file
initialcomp();
     fileOutput.close();
private void initialcomp()
slope=0.0;
intb=0.0;
corr=0.0;
r_sqrt=0.0;
sumx=0.0; sumy=0.0; multixy=0.0; square_x_sum=0.0; square_y_sum=0.0;
for(int i=0;i<data.length;i++)
for(int j=0;j<data[i].length;j++)
data[i][j]=null;
/* MAIN METHOD */
public static void main(String[] args) throws IOException
     // Create instance of class FileChooser
     FileReduction1 newFile = new FileReduction1("File Reduction Program");
     // Make window vissible
     newFile.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
     newFile.setSize(500,400);
newFile.setVisible(true);
Sorry about the long lines.
As you can see, all input files saved in array called files, however when OpenFile1() function is called, it take input (fileName_in) as a single file not an array. I'm assuming this causes the exception.
When there's muptiple inputs, program should take each file from getFileName() to outputToFile() sequentially.
Does anybody have an idea to solve this?
Thanks a lot!!

Answer 1

you naming convention is confussing. you should follows Java naming convention..you have a getXXX but decalred the return type as "void"...get usully means to return something...
your code is doing too much..and hard to follows..
1. get the selected files
for each selected file
process the file and return the result
write out the result.
/** close the precious resource */
public void closeResource(Reader in){
    if (in != null){
        try{ in.close(); }
        catch (Exception e){}
/** get the total number of line in a file */
public int getLineCount(File file) throws IOException{
    BufferedReader in = null;
    int lineCount = 0;
    try{
        in = new BufferedReader(new FileReader(file));
        while ((in.readLine() != null)
            lineCount++;
        return lineCount;
    finally{ closeResource (in);  }
/** read the file */
public void processFile(File inFile, File outFile) throws IOException{
    BufferedReader in = null;
    StringBuffer result = new StringBuffer();
    try{
        in = new BufferedReader(new FileReader(inFile));
        String line = null;
        while ((in.readLine() != null){
            .. do something with the line
            result.append(....);
        writeToFile(outFile, result.toString());
    finally{ closeResource (in);  }
public void writeToFile(File outFile, String result) throws IOException{
    PrintWriter out = null;
    try{
        out = new PrintWriter(new FileWriter(outFile, true));  // true for appending to the end of the file
        out.println(result);
    finally{  if (out != null){ try{ out.close(); } catch (Exception e){} }  }
}