Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException

i am getting a really weird error message in my code, it comes after i have selected a file, the error is :

Code:

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Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
        at java.text.AttributedString.<init>(AttributedString.java:127)
        at PrintText.print(PrintText.java:109)
        at sun.print.RasterPrinterJob.printPage(RasterPrinterJob.java:1973)
        at sun.print.RasterPrinterJob.print(RasterPrinterJob.java:1461)
        at sun.print.RasterPrinterJob.print(RasterPrinterJob.java:1277)
        at PrintText.printer(PrintText.java:98)
        at PrintText$1.run(PrintText.java:52)
        at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:251)
        at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:721)
        at java.awt.EventQueue.access$200(EventQueue.java:103)
        at java.awt.EventQueue$3.run(EventQueue.java:682)
        at java.awt.EventQueue$3.run(EventQueue.java:680)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:691)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:244)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:163)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:151)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:147)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:139)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:97)

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The code :

Code:

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    import java.awt.*;
    import java.awt.font.*;
    import java.awt.geom.*;
    import java.awt.print.*;
    import java.text.*;
    import java.io.*;
    import javax.swing.*;
    import java.util.List;
    import java.util.ArrayList;
   
    public class PrintText implements Printable {
   
        private List<String> list;
   
        // Below the code will allow the user to select a file and then print out the contents of the file
        public static void main(String[] args) throws IOException {
            new PrintText();
        }
   
        public PrintText() {
            EventQueue.invokeLater(new Runnable() {
                    @Override
                    public void run() {
                        try {
                            UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                        } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                        }
   
                        //selects the file
                        JFileChooser chooser = new JFileChooser();
                        chooser.showOpenDialog(null);
                        File file = chooser.getSelectedFile();
                        String filename = file.getName();
                        //System.out.println("You have selected: " + filename);  testing to see if file seleected was right
                        String path = file.getAbsolutePath();
   
                        //Reads contents of file into terminal
                        //FileReader fr = new FileReader("filename");
                        // FileReader fr = new FileReader("D:/Documents/" + "filename"));
   
                        BufferedReader br = null;
                        try {
                            br = new BufferedReader(new FileReader(path));
                            List<String> list = new ArrayList<String>();
                            String line;
                            while ((line = br.readLine()) != null) {
                                System.out.println(line);
                                list.add(line);
                            }
   
                            printer();
                        } catch (IOException exp) {
                            exp.printStackTrace();
                        } finally {
                            try {
                                br.close();
                            } catch (Exception e) {
                            }
                        }
                        //fr.close();
                    }
                });
        }
        //private static final String mText =
        //    "This is a test to see if this text will be printed "; //This works perfectly fine
        //AttributedString mStyledText = new AttributedString(mText);
        /**
        * Print a single page containing some sample text.
        */
        public void printer() {
   
            /* Get the representation of the current printer and
            * the current print job.
            */
            PrinterJob printerJob = PrinterJob.getPrinterJob();
            /* Build a book containing pairs of page painters (Printables)
            * and PageFormats. This example has a single page containing
            * text.
            */
            Book book = new Book();
            book.append(this, new PageFormat());
            /* Set the object to be printed (the Book) into the PrinterJob.
            * Doing this before bringing up the print dialog allows the
            * print dialog to correctly display the page range to be printed
            * and to dissallow any print settings not appropriate for the
            * pages to be printed.
            */
            printerJob.setPageable(book);
            /* Show the print dialog to the user. This is an optional step
            * and need not be done if the application wants to perform
            * 'quiet' printing. If the user cancels the print dialog then false
            * is returned. If true is returned we go ahead and print.
            */
            boolean doPrint = printerJob.printDialog();
            if (doPrint) {
                try {
                    printerJob.print();
                } catch (PrinterException exception) {
                    System.err.println("Printing error: " + exception);
                }
            }
        }
   
        /**
        * Print a page of text.
        */
        public int print(Graphics g, PageFormat format, int pageIndex) {
   
            System.out.println("About to obtain an attributed string, list=" + list);
            AttributedString mStyledText = new AttributedString(list);
            // etc
            /* We'll assume that Jav2D is available.
            */
            Graphics2D g2d = (Graphics2D) g;
            /* Move the origin from the corner of the Paper to the corner
            * of the imageable area.
            */
            g2d.translate(format.getImageableX(), format.getImageableY());
            /* Set the text color.
            */
            g2d.setPaint(Color.black);
            /* Use a LineBreakMeasurer instance to break our text into
            * lines that fit the imageable area of the page.
            */
            Point2D.Float pen = new Point2D.Float();
            AttributedCharacterIterator charIterator = mStyledText.getIterator();
            LineBreakMeasurer measurer = new LineBreakMeasurer(charIterator, g2d.getFontRenderContext());
            float wrappingWidth = (float) format.getImageableWidth();
            while (measurer.getPosition() < charIterator.getEndIndex()) {
                TextLayout layout = measurer.nextLayout(wrappingWidth);
                pen.y += layout.getAscent();
                float dx = layout.isLeftToRight() ? 0 : (wrappingWidth - layout.getAdvance());
                layout.draw(g2d, pen.x + dx, pen.y);
                pen.y += layout.getDescent() + layout.getLeading();
            }
            return Printable.PAGE_EXISTS;
        }
    }

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Quote:

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Code:

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Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at java.text.AttributedString.<init>(AttributedString.java:127)
    at PrintText.print(PrintText.java:109)
    etc

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You read the stack trace from the top down until you hit a line of your code. That's a good place to begin looking for the problem.

In this case it's line 109 which I assume is this one:

Code:

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AttributedString mStyledText = new AttributedString(mText);

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According to the API docs this constructor will throw a NullPointerException if you pass it a null string. It is easy to test if this is happening:

Code:

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public int print(Graphics g, PageFormat format, int pageIndex) {
    System.out.println("About to obtain an attributed string, mText=" + mText);
    AttributedString mStyledText = new AttributedString(mText);
    // etc

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If it turns out that mText is, indeed, null you should go back through your code code to where you thought you had assigned it a non null value and figure out why that didn't happen.

Quote:

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Originally Posted by pbrockway2

You read the stack trace from the top down until you hit a line of your code. That's a good place to begin looking for the problem.

In this case it's line 109 which I assume is this one:

Code:

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AttributedString mStyledText = new AttributedString(mText);

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According to the API docs this constructor will throw a NullPointerException if you pass it a null string. It is easy to test if this is happening:

Code:

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public int print(Graphics g, PageFormat format, int pageIndex) {
    System.out.println("About to obtain an attributed string, mText=" + mText);
    AttributedString mStyledText = new AttributedString(mText);
    // etc

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If it turns out that mText is, indeed, null you should go back through your code code to where you thought you had assigned it a non null value and figure out why that didn't happen.

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You are correct, it turned out to be mText=null

i had thought that in the first part of my code :

Code:

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BufferedReader br = null;
                    try {
                        br = new BufferedReader(new FileReader(path));
                        List<String> list = new ArrayList<String>();
                        while ((mText = br.readLine()) != null) {
                            //Displays the contents of the file in terminal
                            System.out.println(mText);
                            list.add(mText);
                        }

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Would give mText the value of the contents of the file, is this doing this correct?,

Edit

mText is equal to null to end the loop, i have had to use the list and pass this, hopefully this will work

Yes, you are right: the text contents of the file end up in the list, not in mText. mText is a sort of "throw away" variable which is used to add a line to the list and, because of its temporary use, it might have been better to use a local variable in the method that did the reading. That way you would not have been tempted to use it elsewhere.

AttributedString will want some text (a String), not a list. So you are going to hve to put the pieces of the list back together again. It might have been better to use something like a StringBuffer to hold text rather than a list of strings. (Unless you actually want the list elsewhere - I haven't looked at the code that closely).

i have now updated the original post with my current code, i am now having one issue where i can not compile the code, it gives me an error no suitable constructor found for AttributedString(java.util.List<java.lang.String>)

i am told it is because i am passing the entire list of strings instead of a single string.

how can i change my code so it can compile and work ?

Did you understand what I said about reconstructing the text (as a String) from the list?

Code:

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Make a string buffer
for each string in the list
    add it to the string buffer
    add a newline to the buffer
Obtain a String from the StringBuffer

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Alternatively, don't use a list at all. Instead read the text into a string buffer.

Code:

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BufferedReader br = null;
try {
    br = new BufferedReader(new FileReader(path));
    Create a string buffer
    String line;
    while ((line = br.readLine()) != null) {
        Append string to string buffer
        Append newline to string buffer
    }
    Obtain a String from the StringBuffer
    printer(); // or whatever it takes to print the string
} catch (IOException exp) {
    // etc

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The StringBuffer API docs might help. And/or look in Oracle's or some other tutorial for examples of StringBuffer usage.

I have not really looked at the printing in detail, so I can't say more than that using a string buffer yields a string with more or less the content of the original file. So it's worth a try. There may be other problems with the printing, but it's a place to start.

[Edit] And, please, don't edit code once it's posted. Other people reading the thread will have an impossible time figuring out what is what. No-one will mind if you post updated versions of the code: in fact, it's more or less expected.

Ok thanks for all the help, the code is now working well with no errors :) thanks for all your guys help !

You're welcome.