JTable causes my application to crash

Question

I am creating a fairly simple application for a school project. It's a contact manager. I want to display all the contacts in a table, I never used JTables before and it's confusing the crap out of me. I have done lots of research, I only found one thread with the same problem as me but it had no answer or anything helpful.

JVM crash when using JTable

Here's my code to create a table. Just a heads up, I am not looking to create anything complicated. Just a table where I can insert and remove data. That's all.

String[] columnLabels = {"Name", "Number", "Email", "Address"};
Object[][] data = {{"test 1", "test 2"}, {"test 3", "test 4"}};

JTable table = new JTable(data, columnLabels);

If I just insert

JTable table = new JTable(10,4);

Then it will work just fine. Maybe someone can shed some light because I do not know what's wrong. Thanks <3

Here is what the console tells me btw:

Exception in thread "AWT-EventQueue-0" java.lang.ArrayIndexOutOfBoundsException: 2
at javax.swing.JTable$1.getValueAt(Unknown Source)
at javax.swing.JTable.getValueAt(Unknown Source)
at javax.swing.JTable.prepareRenderer(Unknown Source)
at javax.swing.plaf.basic.BasicTableUI.paintCell(Unknown Source)
at javax.swing.plaf.basic.BasicTableUI.paintCells(Unknown Source)
at javax.swing.plaf.basic.BasicTableUI.paint(Unknown Source)
at javax.swing.plaf.ComponentUI.update(Unknown Source)
at javax.swing.JComponent.paintComponent(Unknown Source)
at javax.swing.JComponent.paint(Unknown Source)
at javax.swing.JComponent.paintChildren(Unknown Source)
at javax.swing.JComponent.paint(Unknown Source)
at javax.swing.JViewport.paint(Unknown Source)
at javax.swing.JComponent.paintChildren(Unknown Source)
at javax.swing.JComponent.paint(Unknown Source)
at javax.swing.JComponent.paintChildren(Unknown Source)
at javax.swing.JComponent.paint(Unknown Source)
at javax.swing.JComponent.paintChildren(Unknown Source)
at javax.swing.JComponent.paint(Unknown Source)
at javax.swing.JLayeredPane.paint(Unknown Source)
at javax.swing.JComponent.paintChildren(Unknown Source)
at javax.swing.JComponent.paintToOffscreen(Unknown Source)
at javax.swing.RepaintManager$PaintManager.paintDoubleBuffered(Unknown Source)
at javax.swing.RepaintManager$PaintManager.paint(Unknown Source)
at javax.swing.RepaintManager.paint(Unknown Source)
at javax.swing.JComponent.paint(Unknown Source)
at java.awt.GraphicsCallback$PaintCallback.run(Unknown Source)
at sun.awt.SunGraphicsCallback.runOneComponent(Unknown Source)
at sun.awt.SunGraphicsCallback.runComponents(Unknown Source)
at java.awt.Container.paint(Unknown Source)
at java.awt.Window.paint(Unknown Source)
at javax.swing.RepaintManager$4.run(Unknown Source)
at javax.swing.RepaintManager$4.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
at javax.swing.RepaintManager.prePaintDirtyRegions(Unknown Source)
at javax.swing.RepaintManager.access$1200(Unknown Source)
at javax.swing.RepaintManager$ProcessingRunnable.run(Unknown Source)
at java.awt.event.InvocationEvent.dispatch(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$500(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(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)

Answer 1

You're model array contains 2 rows with 2 columns while your column names array contains 4 elements, hence 4 columns. That's the problem. Provide a data array with 4 elements per row (may be null) and it should work.

From the source of the constructor you're using:

 public int getRowCount() { return rowData.length; }
 public int getColumnCount() { return columnNames.length; }
 public Object getValueAt(int row, int col) { return rowData[row][col]; }

As you can see the renderer looks at the length of columnNames for the number of columns (4 here) and iterates over that (so 0 - 3). Eventually it calls getValueAt(0, 2) and this in turn calls rowData[0][2] and - boom - the col index is out of bounds.

In contrast JTable table = new JTable(10,4); just creates a table with an empty model of 10 rows and 4 columns:

public JTable(int numRows, int numColumns) {
    this(new DefaultTableModel(numRows, numColumns));
}