JTable Exception/Question

[Ray]

My program seems to be having a problem rendering a table. I am not
sure if it has to do with my table model or if I have not implemented
the JTable correctly. I am trying to debug this, but my debugging
skills are lacking at this point. Any feedback appreciated. I have
included code/error below. Also, can a table's rows/cols have an index
of zero (0) or must they begin at one (1)?

tia,

Ray

########################################################################################################

public class XTable extends JFrame {
JTable table;

public XTable() {
super("X Table");
setSize(800, 222);

table = new JTable( new EmitterTableModel(Data.getData()) );

//table.setAutoResizeMode(JTable.AUTO_RESIZE_OFF);
JScrollPane scroll = new JScrollPane( table );
getContentPane().add(scroll, BorderLayout.CENTER);
}

public static void main(String[] args) {
XTable frame = new XTable();
frame.addWindowListener( new WindowAdapter() {
public void windowClosing( WindowEvent e ) {
System.exit(0);
}
});
frame.setVisible(true);
}
}

########################################################################################################

public class EmitterTableModel extends AbstractTableModel {
private final int PRIORITY = 1;
private final int AZIMUTH = 2;

private Emitter[] m_data; // Reference to the data.

private final Object[] column = new Object[] {
"Priority",
"Azimuth",
};

public EmitterTableModel(Emitter[] data) {
m_data = data; // Store a reference to the data.
}

public int getRowCount() { return m_data.length; }
public int getColumnCount() { return column.length; }
public String getColumnName(int col) { return (String) column[col]; }

public Object getValueAt(int row, int col) {
// Get the emitter specified by the row ...
Emitter emitter = m_data[row];

// Get the field specified by the column...
Object rv = null;
//try {
switch ( col ) {
case PRIORITY : rv = new Integer( emitter.getPriority() );
break;
case AZIMUTH : rv = new Double( emitter.getAzimuth() );
break;
default : rv = null; break;
}
//} catch (NullPointerException e) {
// System.out.println(e.printStackTrace());
//}

return rv;
}

// Define the classes returned for each column
public Class getColumnClass( int col ) {
Class rv = null;
switch ( col ) {
case PRIORITY : rv = Integer.class; break;
case AZIMUTH : rv = Double.class; break;
default: rv = null; break;
}
return rv;
}

public void setValueAt(Object obj, int row, int col) {
Emitter emitter = m_data[row];

switch ( col ) {
case PRIORITY : emitter.setPriority( ((Integer)
obj).intValue() ); break;
case AZIMUTH : emitter.setAzimuth( ((Double)
obj).doubleValue() ); break;
default : break;
}
}
}

########################################################################################################

public class Emitter {
private int priority;
private double azimuth;

public Emitter(int p) {
priority = p;
azimuth = 0.0;
}

public Emitter(int p, double az) {
priority = p;
azimuth = az;
}

public int getPriority() { return priority; }
public double getAzimuth() { return azimuth; }

public void setPriority(int value) { priority = value; }
public void setAzimuth(double value) { azimuth = value; }
}

########################################################################################################

Exception occurred during event dispatching:

java.lang.NullPointerException

at javax.swing.JTable.prepareRenderer(JTable.java:3537)

at javax.swing.plaf.basic.BasicTableUI.paintCell(BasicTableUI.java:995)

at
javax.swing.plaf.basic.BasicTableUI.paintCells(BasicTableUI.java:917)

at javax.swing.plaf.basic.BasicTableUI.paint(BasicTableUI.java:858)

at javax.swing.plaf.ComponentUI.update(ComponentUI.java:39)

at javax.swing.JComponent.paintComponent(JComponent.java:398)

at javax.swing.JComponent.paint(JComponent.java:739)

at javax.swing.JComponent.paintChildren(JComponent.java:523)

at javax.swing.JComponent.paint(JComponent.java:748)

at javax.swing.JViewport.paint(JViewport.java:668)

at javax.swing.JComponent.paintWithBuffer(JComponent.java:4393)

at javax.swing.JComponent._paintImmediately(JComponent.java:4336)

at javax.swing.JComponent.paintImmediately(JComponent.java:4187)

at
javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:370)

at
javax.swing.SystemEventQueueUtilities$ComponentWorkRequest.run(SystemEventQueueUtilities.java:205)

at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:154)

at java.awt.EventQueue.dispatchEvent(EventQueue.java:317)

at
java.awt.EventDispatchThread.pumpOneEvent(EventDispatchThread.java:103)

at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)

at java.awt.EventDispatchThread.run(EventDispatchThread.java:84)

[Ray]

I have narrowed my problem down to the getValueAt method. I am trying
to set the Object rv and am getting a java.lang.NullPointerException
error. What am I doing incorrectly in trying to set this object?

Ray

[Christian Kaufhold]

Ray <yarz...@frontiernet.net> wrote:

> My program seems to be having a problem rendering a table. I am not
> sure if it has to do with my table model or if I have not implemented
> the JTable correctly. I am trying to debug this, but my debugging
> skills are lacking at this point. Any feedback appreciated. I have
> included code/error below. Also, can a table's rows/cols have an index
> of zero (0) or must they begin at one (1)?

They *do always begin* at 0 (like arrays, Lists, ListModels etc.) and that
is also your problem.

> public class EmitterTableModel extends AbstractTableModel {
> private final int PRIORITY = 1;
> private final int AZIMUTH = 2;
>
> private Emitter[] m_data; // Reference to the data.
>
> private final Object[] column = new Object[] {
> "Priority",
> "Azimuth",
> };
>
> public EmitterTableModel(Emitter[] data) {
> m_data = data; // Store a reference to the data.
> }
>
> public int getRowCount() { return m_data.length; }
> public int getColumnCount() { return column.length; }

Returns 2: there are the columns '0' and '1'.

> public String getColumnName(int col) { return (String) column[col]; }

Returns "Priority" for col == 0, "Azimuth" for col == 1.

> public Object getValueAt(int row, int col) {

col will be either 0 or 1.

> // Get the emitter specified by the row ...
> Emitter emitter = m_data[row];
>
> // Get the field specified by the column...
> Object rv = null;
> //try {
> switch ( col ) {
> case PRIORITY : rv = new Integer( emitter.getPriority() );
> break;
> case AZIMUTH : rv = new Double( emitter.getAzimuth() );

Never reached, since col is either 0 or 1.

> break;
> default : rv = null; break;

If col is 0, 'null' will be returned. This is still allowed, but not
what you want.

> public Class getColumnClass( int col ) {
> Class rv = null;
> switch ( col ) {
> case PRIORITY : rv = Integer.class; break;
> case AZIMUTH : rv = Double.class; break;
> default: rv = null; break;

But here, if col is 0, you return 'null' for getColumnClass, and that
is invalid.
-> crash.

So fix your constants to be 0-based instead of 1-based.

Christian
--
Your mornings will be brighter
Break the line
Tear up rules
Make the most of a million times no Bauhaus, Hope

[Ray]

Correct. This was half my problem. The other being that you get null
pointer exception whenever you trying assigning a value to an object
that is null (not initialized) or something to this effect.