Databases
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  1. PO
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    <p>Try the following:</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); // NOTE the order below has been flipped!!!! createExcelSheet (log,"C:/Log.xlsx", "Log"); createExcelSheet(sheet,"C:/Spreadsheet.xlsx", "Spreadsheet"); crossReference.addActionListener(new crossReferenceButtonListener()); generateHPD.addActionListener(new generateHPDButtonListener()); } </code></pre> <p>In your original code, you create the button and then add the action listener:</p> <pre><code>crossReference.addActionListener(new crossReferenceButtonListener()); </code></pre> <p>However, it's only after adding the <code>crossReferenceButtonListener</code> that you call <code>createExcelSheet</code>, which is where the <code>Workbook</code>s are actually being instantiated. And that <code>crossReferenceButtonListener</code> wanted to use fields on the <code>Workbook</code>s, but they were null, thus your <code>NullPointerException</code>.</p> <p>By calling the <code>createExcelSheet</code> methods before you add that <code>crossReferenceButtonListener</code>, you will ensure that both <code>log</code> and <code>sheet</code> have been created by the time the <code>crossReferenceButtonListener</code> tries to use 'em.</p>
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    1. POread inserted data from excel spreadsheet while program execution POI, JAVA
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    1. USakokskis
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      1. VTUpMod
    1. COthis helped but did not solve the problem. or I would say just solved it partially. Thanx
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      1. USJenny
    2. COHowever there is another problem a much deeper one. When the 2 workbooks open on my desktop they are new and empty. I enter data and click 'save' but the data dont seem to be saved. because now when I run int rowNum = ws.getLastRowNum(); it throws an exception
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Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

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