StackOverflow2013

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POread inserted data from excel spreadsheet while program execution POI, JAVA
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copied!<p>I am creating an application that reads excel file into the programs and manipulates them. Before now, everything worked fine. But when I stareted implementing the GUI for my application it does not work anymore.</p> <p>here is the code:</p> <p>when the program launches it creates a gui with buttons and opens 2 new spreadsheets. I enter data in those spreadsheets and then press the button that calls crossReferenceButtonListener, however it fails to get the data out. error message below</p> <pre><code>public GUI () throws Exception{ this.setTitle("NYWM Cross Reference Application"); this.setSize(400,100); this.setVisible(true); this.setLocationRelativeTo(null); buttonHolder = new Panel (new BorderLayout()); this.add(buttonHolder); crossReference = new Button ("CrossReference"); generateHPD = new Button ("Generate HPD"); buttonHolder.add(crossReference, BorderLayout.NORTH); buttonHolder.add(generateHPD, BorderLayout.SOUTH); crossReference.addActionListener(new crossReferenceButtonListener()); generateHPD.addActionListener(new generateHPDButtonListener()); createExcelSheet (log,"C:/Log.xlsx", "Log"); createExcelSheet(sheet,"C:/Spreadsheet.xlsx", "Spreadsheet"); } private void createExcelSheet (XSSFWorkbook wb, String path, String fileName) throws Exception{ try{ FileOutputStream out = new FileOutputStream (path); wb = new XSSFWorkbook (); XSSFSheet sheet = wb.createSheet(fileName); wb.write(out); Process p = Runtime.getRuntime().exec( "rundll32 url.dll, FileProtocolHandler " + path); } catch (Exception e){ throw e; } } private class crossReferenceButtonListener implements ActionListener { public void actionPerformed (ActionEvent event){ try { ref = new CrossReference (log.getSheet("Log"), sheet.getSheet("Spreadsheet")); ref.CrossReference(); JOptionPane.showMessageDialog(null, "Cross Reference was successful!"); } catch (Exception e) { // TODO Auto-generated catch block e.printStackTrace(); } } } </code></pre> <p>error message: to be more specific, it fails at this line </p> <pre><code> ref = new CrossReference (log.getSheet("Log"), sheet.getSheet("Spreadsheet")); </code></pre> <p>error:</p> <pre><code>at java.awt.EventDispatchThread.run(Unknown Source) java.lang.NullPointerException at nywm_crossReferenceApplication.GUI$crossReferenceButtonListener.actionPerformed(GUI.java:70) at java.awt.Button.processActionEvent(Unknown Source) at java.awt.Button.processEvent(Unknown Source) at java.awt.Component.dispatchEventImpl(Unknown Source) at java.awt.Component.dispatchEvent(Unknown Source) at java.awt.EventQueue.dispatchEvent(Unknown Source) at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source) at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source) at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source) at java.awt.EventDispatchThread.pumpEvents(Unknown Source) at java.awt.EventDispatchThread.pumpEvents(Unknown Source) at java.awt.EventDispatchThread.run(Unknown Source) </code></pre>

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